coccinelle: alloc_cast: drop removed allocatorsgrafted

- pci_alloc_consistent() and pci_zalloc_consistent() were removed by
  commit 7968778914e5
  ("PCI: Remove the deprecated "pci-dma-compat.h" API")

- kmem_alloc() was removed by commit f078d4ea8276
  ("xfs: convert kmem_alloc() to kmalloc()")

- kmem_zalloc() was removed by commit 10634530f7ba
  ("xfs: convert kmem_zalloc() to kzalloc()")

- kmem_zone_alloc() and kmem_zone_zalloc() were removed by commit
  bae633a4a283 ("xfs: remove xfs_zone_{alloc,zalloc} helpers")

So drop them from the rules.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

1 files changed, 7683 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
new file mode 100644
index 000000000..8da0f9451
--- /dev/null
+++ b/mm/memory.c
@@ -0,0 +1,7683 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/mm/memory.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ */
+
+/*
+ * demand-loading started 01.12.91 - seems it is high on the list of
+ * things wanted, and it should be easy to implement. - Linus
+ */
+
+/*
+ * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
+ * pages started 02.12.91, seems to work. - Linus.
+ *
+ * Tested sharing by executing about 30 /bin/sh: under the old kernel it
+ * would have taken more than the 6M I have free, but it worked well as
+ * far as I could see.
+ *
+ * Also corrected some "invalidate()"s - I wasn't doing enough of them.
+ */
+
+/*
+ * Real VM (paging to/from disk) started 18.12.91. Much more work and
+ * thought has to go into this. Oh, well..
+ * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
+ *		Found it. Everything seems to work now.
+ * 20.12.91  -  Ok, making the swap-device changeable like the root.
+ */
+
+/*
+ * 05.04.94  -  Multi-page memory management added for v1.1.
+ *              Idea by Alex Bligh (alex@cconcepts.co.uk)
+ *
+ * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
+ *		(Gerhard.Wichert@pdb.siemens.de)
+ *
+ * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
+ */
+
+#include <linux/kernel_stat.h>
+#include <linux/mm.h>
+#include <linux/mm_inline.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/numa_balancing.h>
+#include <linux/sched/task.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>
+#include <linux/memremap.h>
+#include <linux/kmsan.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/export.h>
+#include <linux/delayacct.h>
+#include <linux/init.h>
+#include <linux/writeback.h>
+#include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
+#include <linux/leafops.h>
+#include <linux/elf.h>
+#include <linux/gfp.h>
+#include <linux/migrate.h>
+#include <linux/string.h>
+#include <linux/shmem_fs.h>
+#include <linux/memory-tiers.h>
+#include <linux/debugfs.h>
+#include <linux/userfaultfd_k.h>
+#include <linux/dax.h>
+#include <linux/oom.h>
+#include <linux/numa.h>
+#include <linux/perf_event.h>
+#include <linux/ptrace.h>
+#include <linux/vmalloc.h>
+#include <linux/sched/sysctl.h>
+#include <linux/pgalloc.h>
+#include <linux/uaccess.h>
+
+#include <trace/events/kmem.h>
+
+#include <asm/io.h>
+#include <asm/mmu_context.h>
+#include <asm/tlb.h>
+#include <asm/tlbflush.h>
+
+#include "pgalloc-track.h"
+#include "internal.h"
+#include "swap.h"
+
+#if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
+#warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
+#endif
+
+static vm_fault_t do_fault(struct vm_fault *vmf);
+static vm_fault_t do_anonymous_page(struct vm_fault *vmf);
+static bool vmf_pte_changed(struct vm_fault *vmf);
+
+/*
+ * Return true if the original pte was a uffd-wp pte marker (so the pte was
+ * wr-protected).
+ */
+static __always_inline bool vmf_orig_pte_uffd_wp(struct vm_fault *vmf)
+{
+	if (!userfaultfd_wp(vmf->vma))
+		return false;
+	if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID))
+		return false;
+
+	return pte_is_uffd_wp_marker(vmf->orig_pte);
+}
+
+/*
+ * Randomize the address space (stacks, mmaps, brk, etc.).
+ *
+ * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
+ *   as ancient (libc5 based) binaries can segfault. )
+ */
+int randomize_va_space __read_mostly =
+#ifdef CONFIG_COMPAT_BRK
+					1;
+#else
+					2;
+#endif
+
+static const struct ctl_table mmu_sysctl_table[] = {
+	{
+		.procname	= "randomize_va_space",
+		.data		= &randomize_va_space,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+};
+
+static int __init init_mm_sysctl(void)
+{
+	register_sysctl_init("kernel", mmu_sysctl_table);
+	return 0;
+}
+
+subsys_initcall(init_mm_sysctl);
+
+#ifndef arch_wants_old_prefaulted_pte
+static inline bool arch_wants_old_prefaulted_pte(void)
+{
+	/*
+	 * Transitioning a PTE from 'old' to 'young' can be expensive on
+	 * some architectures, even if it's performed in hardware. By
+	 * default, "false" means prefaulted entries will be 'young'.
+	 */
+	return false;
+}
+#endif
+
+static int __init disable_randmaps(char *s)
+{
+	randomize_va_space = 0;
+	return 1;
+}
+__setup("norandmaps", disable_randmaps);
+
+unsigned long highest_memmap_pfn __read_mostly;
+
+void mm_trace_rss_stat(struct mm_struct *mm, int member)
+{
+	trace_rss_stat(mm, member);
+}
+
+/*
+ * Note: this doesn't free the actual pages themselves. That
+ * has been handled earlier when unmapping all the memory regions.
+ */
+static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
+			   unsigned long addr)
+{
+	pgtable_t token = pmd_pgtable(*pmd);
+	pmd_clear(pmd);
+	pte_free_tlb(tlb, token, addr);
+	mm_dec_nr_ptes(tlb->mm);
+}
+
+static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(pmd))
+			continue;
+		free_pte_range(tlb, pmd, addr);
+	} while (pmd++, addr = next, addr != end);
+
+	start &= PUD_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= PUD_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	pmd = pmd_offset(pud, start);
+	pud_clear(pud);
+	pmd_free_tlb(tlb, pmd, start);
+	mm_dec_nr_pmds(tlb->mm);
+}
+
+static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	pud_t *pud;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		free_pmd_range(tlb, pud, addr, next, floor, ceiling);
+	} while (pud++, addr = next, addr != end);
+
+	start &= P4D_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= P4D_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	pud = pud_offset(p4d, start);
+	p4d_clear(p4d);
+	pud_free_tlb(tlb, pud, start);
+	mm_dec_nr_puds(tlb->mm);
+}
+
+static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		free_pud_range(tlb, p4d, addr, next, floor, ceiling);
+	} while (p4d++, addr = next, addr != end);
+
+	start &= PGDIR_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= PGDIR_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	p4d = p4d_offset(pgd, start);
+	pgd_clear(pgd);
+	p4d_free_tlb(tlb, p4d, start);
+}
+
+/**
+ * free_pgd_range - Unmap and free page tables in the range
+ * @tlb: the mmu_gather containing pending TLB flush info
+ * @addr: virtual address start
+ * @end: virtual address end
+ * @floor: lowest address boundary
+ * @ceiling: highest address boundary
+ *
+ * This function tears down all user-level page tables in the
+ * specified virtual address range [@addr..@end). It is part of
+ * the memory unmap flow.
+ */
+void free_pgd_range(struct mmu_gather *tlb,
+			unsigned long addr, unsigned long end,
+			unsigned long floor, unsigned long ceiling)
+{
+	pgd_t *pgd;
+	unsigned long next;
+
+	/*
+	 * The next few lines have given us lots of grief...
+	 *
+	 * Why are we testing PMD* at this top level?  Because often
+	 * there will be no work to do at all, and we'd prefer not to
+	 * go all the way down to the bottom just to discover that.
+	 *
+	 * Why all these "- 1"s?  Because 0 represents both the bottom
+	 * of the address space and the top of it (using -1 for the
+	 * top wouldn't help much: the masks would do the wrong thing).
+	 * The rule is that addr 0 and floor 0 refer to the bottom of
+	 * the address space, but end 0 and ceiling 0 refer to the top
+	 * Comparisons need to use "end - 1" and "ceiling - 1" (though
+	 * that end 0 case should be mythical).
+	 *
+	 * Wherever addr is brought up or ceiling brought down, we must
+	 * be careful to reject "the opposite 0" before it confuses the
+	 * subsequent tests.  But what about where end is brought down
+	 * by PMD_SIZE below? no, end can't go down to 0 there.
+	 *
+	 * Whereas we round start (addr) and ceiling down, by different
+	 * masks at different levels, in order to test whether a table
+	 * now has no other vmas using it, so can be freed, we don't
+	 * bother to round floor or end up - the tests don't need that.
+	 */
+
+	addr &= PMD_MASK;
+	if (addr < floor) {
+		addr += PMD_SIZE;
+		if (!addr)
+			return;
+	}
+	if (ceiling) {
+		ceiling &= PMD_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		end -= PMD_SIZE;
+	if (addr > end - 1)
+		return;
+	/*
+	 * We add page table cache pages with PAGE_SIZE,
+	 * (see pte_free_tlb()), flush the tlb if we need
+	 */
+	tlb_change_page_size(tlb, PAGE_SIZE);
+	pgd = pgd_offset(tlb->mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		free_p4d_range(tlb, pgd, addr, next, floor, ceiling);
+	} while (pgd++, addr = next, addr != end);
+}
+
+/**
+ * free_pgtables() - Free a range of page tables
+ * @tlb: The mmu gather
+ * @unmap: The unmap_desc
+ *
+ * Note: pg_start and pg_end are provided to indicate the absolute range of the
+ * page tables that should be removed.  This can differ from the vma mappings on
+ * some archs that may have mappings that need to be removed outside the vmas.
+ * Note that the prev->vm_end and next->vm_start are often used.
+ *
+ * The vma_end differs from the pg_end when a dup_mmap() failed and the tree has
+ * unrelated data to the mm_struct being torn down.
+ */
+void free_pgtables(struct mmu_gather *tlb, struct unmap_desc *unmap)
+{
+	struct unlink_vma_file_batch vb;
+	struct ma_state *mas = unmap->mas;
+	struct vm_area_struct *vma = unmap->first;
+
+	/*
+	 * Note: USER_PGTABLES_CEILING may be passed as the value of pg_end and
+	 * may be 0.  Underflow is expected in this case.  Otherwise the
+	 * pagetable end is exclusive.  vma_end is exclusive.  The last vma
+	 * address should never be larger than the pagetable end.
+	 */
+	WARN_ON_ONCE(unmap->vma_end - 1 > unmap->pg_end - 1);
+
+	tlb_free_vmas(tlb);
+
+	do {
+		unsigned long addr = vma->vm_start;
+		struct vm_area_struct *next;
+
+		next = mas_find(mas, unmap->tree_end - 1);
+
+		/*
+		 * Hide vma from rmap and truncate_pagecache before freeing
+		 * pgtables
+		 */
+		if (unmap->mm_wr_locked)
+			vma_start_write(vma);
+		unlink_anon_vmas(vma);
+
+		unlink_file_vma_batch_init(&vb);
+		unlink_file_vma_batch_add(&vb, vma);
+
+		/*
+		 * Optimization: gather nearby vmas into one call down
+		 */
+		while (next && next->vm_start <= vma->vm_end + PMD_SIZE) {
+			vma = next;
+			next = mas_find(mas, unmap->tree_end - 1);
+			if (unmap->mm_wr_locked)
+				vma_start_write(vma);
+			unlink_anon_vmas(vma);
+			unlink_file_vma_batch_add(&vb, vma);
+		}
+		unlink_file_vma_batch_final(&vb);
+
+		free_pgd_range(tlb, addr, vma->vm_end, unmap->pg_start,
+			       next ? next->vm_start : unmap->pg_end);
+		vma = next;
+	} while (vma);
+}
+
+void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte)
+{
+	spinlock_t *ptl = pmd_lock(mm, pmd);
+
+	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
+		mm_inc_nr_ptes(mm);
+		/*
+		 * Ensure all pte setup (eg. pte page lock and page clearing) are
+		 * visible before the pte is made visible to other CPUs by being
+		 * put into page tables.
+		 *
+		 * The other side of the story is the pointer chasing in the page
+		 * table walking code (when walking the page table without locking;
+		 * ie. most of the time). Fortunately, these data accesses consist
+		 * of a chain of data-dependent loads, meaning most CPUs (alpha
+		 * being the notable exception) will already guarantee loads are
+		 * seen in-order. See the alpha page table accessors for the
+		 * smp_rmb() barriers in page table walking code.
+		 */
+		smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
+		pmd_populate(mm, pmd, *pte);
+		*pte = NULL;
+	}
+	spin_unlock(ptl);
+}
+
+int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
+{
+	pgtable_t new = pte_alloc_one(mm);
+	if (!new)
+		return -ENOMEM;
+
+	pmd_install(mm, pmd, &new);
+	if (new)
+		pte_free(mm, new);
+	return 0;
+}
+
+int __pte_alloc_kernel(pmd_t *pmd)
+{
+	pte_t *new = pte_alloc_one_kernel(&init_mm);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&init_mm.page_table_lock);
+	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
+		smp_wmb(); /* See comment in pmd_install() */
+		pmd_populate_kernel(&init_mm, pmd, new);
+		new = NULL;
+	}
+	spin_unlock(&init_mm.page_table_lock);
+	if (new)
+		pte_free_kernel(&init_mm, new);
+	return 0;
+}
+
+static inline void init_rss_vec(int *rss)
+{
+	memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
+}
+
+static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
+{
+	int i;
+
+	for (i = 0; i < NR_MM_COUNTERS; i++)
+		if (rss[i])
+			add_mm_counter(mm, i, rss[i]);
+}
+
+static bool is_bad_page_map_ratelimited(void)
+{
+	static unsigned long resume;
+	static unsigned long nr_shown;
+	static unsigned long nr_unshown;
+
+	/*
+	 * Allow a burst of 60 reports, then keep quiet for that minute;
+	 * or allow a steady drip of one report per second.
+	 */
+	if (nr_shown == 60) {
+		if (time_before(jiffies, resume)) {
+			nr_unshown++;
+			return true;
+		}
+		if (nr_unshown) {
+			pr_alert("BUG: Bad page map: %lu messages suppressed\n",
+				 nr_unshown);
+			nr_unshown = 0;
+		}
+		nr_shown = 0;
+	}
+	if (nr_shown++ == 0)
+		resume = jiffies + 60 * HZ;
+	return false;
+}
+
+static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long addr)
+{
+	unsigned long long pgdv, p4dv, pudv, pmdv;
+	p4d_t p4d, *p4dp;
+	pud_t pud, *pudp;
+	pmd_t pmd, *pmdp;
+	pgd_t *pgdp;
+
+	/*
+	 * Although this looks like a fully lockless pgtable walk, it is not:
+	 * see locking requirements for print_bad_page_map().
+	 */
+	pgdp = pgd_offset(mm, addr);
+	pgdv = pgd_val(*pgdp);
+
+	if (!pgd_present(*pgdp) || pgd_leaf(*pgdp)) {
+		pr_alert("pgd:%08llx\n", pgdv);
+		return;
+	}
+
+	p4dp = p4d_offset(pgdp, addr);
+	p4d = p4dp_get(p4dp);
+	p4dv = p4d_val(p4d);
+
+	if (!p4d_present(p4d) || p4d_leaf(p4d)) {
+		pr_alert("pgd:%08llx p4d:%08llx\n", pgdv, p4dv);
+		return;
+	}
+
+	pudp = pud_offset(p4dp, addr);
+	pud = pudp_get(pudp);
+	pudv = pud_val(pud);
+
+	if (!pud_present(pud) || pud_leaf(pud)) {
+		pr_alert("pgd:%08llx p4d:%08llx pud:%08llx\n", pgdv, p4dv, pudv);
+		return;
+	}
+
+	pmdp = pmd_offset(pudp, addr);
+	pmd = pmdp_get(pmdp);
+	pmdv = pmd_val(pmd);
+
+	/*
+	 * Dumping the PTE would be nice, but it's tricky with CONFIG_HIGHPTE,
+	 * because the table should already be mapped by the caller and
+	 * doing another map would be bad. print_bad_page_map() should
+	 * already take care of printing the PTE.
+	 */
+	pr_alert("pgd:%08llx p4d:%08llx pud:%08llx pmd:%08llx\n", pgdv,
+		 p4dv, pudv, pmdv);
+}
+
+/*
+ * This function is called to print an error when a bad page table entry (e.g.,
+ * corrupted page table entry) is found. For example, we might have a
+ * PFN-mapped pte in a region that doesn't allow it.
+ *
+ * The calling function must still handle the error.
+ *
+ * This function must be called during a proper page table walk, as it will
+ * re-walk the page table to dump information: the caller MUST prevent page
+ * table teardown (by holding mmap, vma or rmap lock) and MUST hold the leaf
+ * page table lock.
+ */
+static void print_bad_page_map(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long long entry, struct page *page,
+		enum pgtable_level level)
+{
+	struct address_space *mapping;
+	pgoff_t index;
+
+	if (is_bad_page_map_ratelimited())
+		return;
+
+	mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
+	index = linear_page_index(vma, addr);
+
+	pr_alert("BUG: Bad page map in process %s  %s:%08llx", current->comm,
+		 pgtable_level_to_str(level), entry);
+	__print_bad_page_map_pgtable(vma->vm_mm, addr);
+	if (page)
+		dump_page(page, "bad page map");
+	pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
+		 (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
+	pr_alert("file:%pD fault:%ps mmap:%ps mmap_prepare: %ps read_folio:%ps\n",
+		 vma->vm_file,
+		 vma->vm_ops ? vma->vm_ops->fault : NULL,
+		 vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
+		 vma->vm_file ? vma->vm_file->f_op->mmap_prepare : NULL,
+		 mapping ? mapping->a_ops->read_folio : NULL);
+	dump_stack();
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+}
+
+static inline bool pgtable_level_has_pxx_special(enum pgtable_level level)
+{
+	switch (level) {
+	case PGTABLE_LEVEL_PTE:
+		return IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL);
+	case PGTABLE_LEVEL_PMD:
+		return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP);
+	case PGTABLE_LEVEL_PUD:
+		return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP);
+	default:
+		return false;
+	}
+}
+
+#define print_bad_pte(vma, addr, pte, page) \
+	print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE)
+
+/**
+ * __vm_normal_page() - Get the "struct page" associated with a page table entry.
+ * @vma: The VMA mapping the page table entry.
+ * @addr: The address where the page table entry is mapped.
+ * @pfn: The PFN stored in the page table entry.
+ * @special: Whether the page table entry is marked "special".
+ * @level: The page table level for error reporting purposes only.
+ * @entry: The page table entry value for error reporting purposes only.
+ *
+ * "Special" mappings do not wish to be associated with a "struct page" (either
+ * it doesn't exist, or it exists but they don't want to touch it). In this
+ * case, NULL is returned here. "Normal" mappings do have a struct page and
+ * are ordinarily refcounted.
+ *
+ * Page mappings of the shared zero folios are always considered "special", as
+ * they are not ordinarily refcounted: neither the refcount nor the mapcount
+ * of these folios is adjusted when mapping them into user page tables.
+ * Selected page table walkers (such as GUP) can still identify mappings of the
+ * shared zero folios and work with the underlying "struct page".
+ *
+ * There are 2 broad cases. Firstly, an architecture may define a "special"
+ * page table entry bit, such as pte_special(), in which case this function is
+ * trivial. Secondly, an architecture may not have a spare page table
+ * entry bit, which requires a more complicated scheme, described below.
+ *
+ * With CONFIG_FIND_NORMAL_PAGE, we might have the "special" bit set on
+ * page table entries that actually map "normal" pages: however, that page
+ * cannot be looked up through the PFN stored in the page table entry, but
+ * instead will be looked up through vm_ops->find_normal_page(). So far, this
+ * only applies to PTEs.
+ *
+ * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
+ * special mapping (even if there are underlying and valid "struct pages").
+ * COWed pages of a VM_PFNMAP are always normal.
+ *
+ * The way we recognize COWed pages within VM_PFNMAP mappings is through the
+ * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
+ * set, and the vm_pgoff will point to the first PFN mapped: thus every special
+ * mapping will always honor the rule
+ *
+ *	pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
+ *
+ * And for normal mappings this is false.
+ *
+ * This restricts such mappings to be a linear translation from virtual address
+ * to pfn. To get around this restriction, we allow arbitrary mappings so long
+ * as the vma is not a COW mapping; in that case, we know that all ptes are
+ * special (because none can have been COWed).
+ *
+ *
+ * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
+ *
+ * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
+ * page" backing, however the difference is that _all_ pages with a struct
+ * page (that is, those where pfn_valid is true, except the shared zero
+ * folios) are refcounted and considered normal pages by the VM.
+ *
+ * The disadvantage is that pages are refcounted (which can be slower and
+ * simply not an option for some PFNMAP users). The advantage is that we
+ * don't have to follow the strict linearity rule of PFNMAP mappings in
+ * order to support COWable mappings.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+static inline struct page *__vm_normal_page(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pfn, bool special,
+		unsigned long long entry, enum pgtable_level level)
+{
+	if (pgtable_level_has_pxx_special(level)) {
+		if (unlikely(special)) {
+#ifdef CONFIG_FIND_NORMAL_PAGE
+			if (vma->vm_ops && vma->vm_ops->find_normal_page)
+				return vma->vm_ops->find_normal_page(vma, addr);
+#endif /* CONFIG_FIND_NORMAL_PAGE */
+			if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+				return NULL;
+			if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
+				return NULL;
+
+			print_bad_page_map(vma, addr, entry, NULL, level);
+			return NULL;
+		}
+		/*
+		 * With working pte_special()/pmd_special()..., any special page
+		 * table mappings (incl. shared zero folios) are marked
+		 * accordingly.
+		 */
+	} else {
+		if (unlikely(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))) {
+			if (vma->vm_flags & VM_MIXEDMAP) {
+				/* If it has a "struct page", it's "normal". */
+				if (!pfn_valid(pfn))
+					return NULL;
+			} else {
+				const pgoff_t index = linear_page_index(vma, addr);
+
+				/* Only CoW'ed anon folios are "normal". */
+				if (pfn == index)
+					return NULL;
+				if (!is_cow_mapping(vma->vm_flags))
+					return NULL;
+			}
+		}
+
+		if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
+			return NULL;
+	}
+
+	if (unlikely(pfn > highest_memmap_pfn)) {
+		/* Corrupted page table entry. */
+		print_bad_page_map(vma, addr, entry, NULL, level);
+		return NULL;
+	}
+	/*
+	 * NOTE! We still have PageReserved() pages in the page tables.
+	 * For example, VDSO mappings can cause them to exist.
+	 */
+	VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn));
+	return pfn_to_page(pfn);
+}
+
+/**
+ * vm_normal_page() - Get the "struct page" associated with a PTE
+ * @vma: The VMA mapping the @pte.
+ * @addr: The address where the @pte is mapped.
+ * @pte: The PTE.
+ *
+ * Get the "struct page" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
+			    pte_t pte)
+{
+	return __vm_normal_page(vma, addr, pte_pfn(pte), pte_special(pte),
+				pte_val(pte), PGTABLE_LEVEL_PTE);
+}
+
+/**
+ * vm_normal_folio() - Get the "struct folio" associated with a PTE
+ * @vma: The VMA mapping the @pte.
+ * @addr: The address where the @pte is mapped.
+ * @pte: The PTE.
+ *
+ * Get the "struct folio" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct folio" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
+			    pte_t pte)
+{
+	struct page *page = vm_normal_page(vma, addr, pte);
+
+	if (page)
+		return page_folio(page);
+	return NULL;
+}
+
+#ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
+/**
+ * vm_normal_page_pmd() - Get the "struct page" associated with a PMD
+ * @vma: The VMA mapping the @pmd.
+ * @addr: The address where the @pmd is mapped.
+ * @pmd: The PMD.
+ *
+ * Get the "struct page" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
+				pmd_t pmd)
+{
+	return __vm_normal_page(vma, addr, pmd_pfn(pmd), pmd_special(pmd),
+				pmd_val(pmd), PGTABLE_LEVEL_PMD);
+}
+
+/**
+ * vm_normal_folio_pmd() - Get the "struct folio" associated with a PMD
+ * @vma: The VMA mapping the @pmd.
+ * @addr: The address where the @pmd is mapped.
+ * @pmd: The PMD.
+ *
+ * Get the "struct folio" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct folio" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
+				  unsigned long addr, pmd_t pmd)
+{
+	struct page *page = vm_normal_page_pmd(vma, addr, pmd);
+
+	if (page)
+		return page_folio(page);
+	return NULL;
+}
+
+/**
+ * vm_normal_page_pud() - Get the "struct page" associated with a PUD
+ * @vma: The VMA mapping the @pud.
+ * @addr: The address where the @pud is mapped.
+ * @pud: The PUD.
+ *
+ * Get the "struct page" associated with a PUD. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct page *vm_normal_page_pud(struct vm_area_struct *vma,
+		unsigned long addr, pud_t pud)
+{
+	return __vm_normal_page(vma, addr, pud_pfn(pud), pud_special(pud),
+				pud_val(pud), PGTABLE_LEVEL_PUD);
+}
+#endif
+
+/**
+ * restore_exclusive_pte - Restore a device-exclusive entry
+ * @vma: VMA covering @address
+ * @folio: the mapped folio
+ * @page: the mapped folio page
+ * @address: the virtual address
+ * @ptep: pte pointer into the locked page table mapping the folio page
+ * @orig_pte: pte value at @ptep
+ *
+ * Restore a device-exclusive non-swap entry to an ordinary present pte.
+ *
+ * The folio and the page table must be locked, and MMU notifiers must have
+ * been called to invalidate any (exclusive) device mappings.
+ *
+ * Locking the folio makes sure that anybody who just converted the pte to
+ * a device-exclusive entry can map it into the device to make forward
+ * progress without others converting it back until the folio was unlocked.
+ *
+ * If the folio lock ever becomes an issue, we can stop relying on the folio
+ * lock; it might make some scenarios with heavy thrashing less likely to
+ * make forward progress, but these scenarios might not be valid use cases.
+ *
+ * Note that the folio lock does not protect against all cases of concurrent
+ * page table modifications (e.g., MADV_DONTNEED, mprotect), so device drivers
+ * must use MMU notifiers to sync against any concurrent changes.
+ */
+static void restore_exclusive_pte(struct vm_area_struct *vma,
+		struct folio *folio, struct page *page, unsigned long address,
+		pte_t *ptep, pte_t orig_pte)
+{
+	pte_t pte;
+
+	VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	pte = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
+	if (pte_swp_soft_dirty(orig_pte))
+		pte = pte_mksoft_dirty(pte);
+
+	if (pte_swp_uffd(orig_pte))
+		pte = pte_mkuffd(pte);
+
+	/* See do_swap_page(): restore PAGE_NONE for RWP */
+	if (pte_swp_uffd(orig_pte) && userfaultfd_rwp(vma))
+		pte = pte_modify(pte, PAGE_NONE);
+
+	if ((vma->vm_flags & VM_WRITE) &&
+	    can_change_pte_writable(vma, address, pte)) {
+		if (folio_test_dirty(folio))
+			pte = pte_mkdirty(pte);
+		pte = pte_mkwrite(pte, vma);
+	}
+	set_pte_at(vma->vm_mm, address, ptep, pte);
+
+	/*
+	 * No need to invalidate - it was non-present before. However
+	 * secondary CPUs may have mappings that need invalidating.
+	 */
+	update_mmu_cache(vma, address, ptep);
+}
+
+/*
+ * Tries to restore an exclusive pte if the page lock can be acquired without
+ * sleeping.
+ */
+static int try_restore_exclusive_pte(struct vm_area_struct *vma,
+		unsigned long addr, pte_t *ptep, pte_t orig_pte)
+{
+	const softleaf_t entry = softleaf_from_pte(orig_pte);
+	struct page *page = softleaf_to_page(entry);
+	struct folio *folio = page_folio(page);
+
+	if (folio_trylock(folio)) {
+		restore_exclusive_pte(vma, folio, page, addr, ptep, orig_pte);
+		folio_unlock(folio);
+		return 0;
+	}
+
+	return -EBUSY;
+}
+
+/*
+ * copy one vm_area from one task to the other. Assumes the page tables
+ * already present in the new task to be cleared in the whole range
+ * covered by this vma.
+ */
+
+static unsigned long
+copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *dst_vma,
+		struct vm_area_struct *src_vma, unsigned long addr, int *rss)
+{
+	vm_flags_t vm_flags = dst_vma->vm_flags;
+	pte_t orig_pte = ptep_get(src_pte);
+	softleaf_t entry = softleaf_from_pte(orig_pte);
+	pte_t pte = orig_pte;
+	struct folio *folio;
+	struct page *page;
+
+	if (likely(softleaf_is_swap(entry))) {
+		if (swap_dup_entry_direct(entry) < 0)
+			return -EIO;
+
+		mm_prepare_for_swap_entries(dst_mm);
+		/* Mark the swap entry as shared. */
+		if (pte_swp_exclusive(orig_pte)) {
+			pte = pte_swp_clear_exclusive(orig_pte);
+			set_pte_at(src_mm, addr, src_pte, pte);
+		}
+		rss[MM_SWAPENTS]++;
+	} else if (softleaf_is_migration(entry)) {
+		folio = softleaf_to_folio(entry);
+
+		rss[mm_counter(folio)]++;
+
+		if (!softleaf_is_migration_read(entry) &&
+				is_cow_mapping(vm_flags)) {
+			/*
+			 * COW mappings require pages in both parent and child
+			 * to be set to read. A previously exclusive entry is
+			 * now shared.
+			 */
+			entry = make_readable_migration_entry(
+							swp_offset(entry));
+			pte = softleaf_to_pte(entry);
+			if (pte_swp_soft_dirty(orig_pte))
+				pte = pte_swp_mksoft_dirty(pte);
+			if (pte_swp_uffd(orig_pte))
+				pte = pte_swp_mkuffd(pte);
+			set_pte_at(src_mm, addr, src_pte, pte);
+		}
+	} else if (softleaf_is_device_private(entry)) {
+		page = softleaf_to_page(entry);
+		folio = page_folio(page);
+
+		/*
+		 * Update rss count even for unaddressable pages, as
+		 * they should treated just like normal pages in this
+		 * respect.
+		 *
+		 * We will likely want to have some new rss counters
+		 * for unaddressable pages, at some point. But for now
+		 * keep things as they are.
+		 */
+		folio_get(folio);
+		rss[mm_counter(folio)]++;
+		/* Cannot fail as these pages cannot get pinned. */
+		folio_try_dup_anon_rmap_pte(folio, page, dst_vma, src_vma);
+
+		/*
+		 * We do not preserve soft-dirty information, because so
+		 * far, checkpoint/restore is the only feature that
+		 * requires that. And checkpoint/restore does not work
+		 * when a device driver is involved (you cannot easily
+		 * save and restore device driver state).
+		 */
+		if (softleaf_is_device_private_write(entry) &&
+		    is_cow_mapping(vm_flags)) {
+			entry = make_readable_device_private_entry(
+							swp_offset(entry));
+			pte = swp_entry_to_pte(entry);
+			if (pte_swp_uffd(orig_pte))
+				pte = pte_swp_mkuffd(pte);
+			set_pte_at(src_mm, addr, src_pte, pte);
+		}
+	} else if (softleaf_is_device_exclusive(entry)) {
+		/*
+		 * Make device exclusive entries present by restoring the
+		 * original entry then copying as for a present pte. Device
+		 * exclusive entries currently only support private writable
+		 * (ie. COW) mappings.
+		 */
+		VM_BUG_ON(!is_cow_mapping(src_vma->vm_flags));
+		if (try_restore_exclusive_pte(src_vma, addr, src_pte, orig_pte))
+			return -EBUSY;
+		return -ENOENT;
+	} else if (softleaf_is_marker(entry)) {
+		pte_marker marker = copy_pte_marker(entry, dst_vma);
+
+		if (marker)
+			set_pte_at(dst_mm, addr, dst_pte,
+				   make_pte_marker(marker));
+		return 0;
+	}
+	if (!userfaultfd_protected(dst_vma))
+		pte = pte_swp_clear_uffd(pte);
+	set_pte_at(dst_mm, addr, dst_pte, pte);
+	return 0;
+}
+
+/*
+ * Copy a present and normal page.
+ *
+ * NOTE! The usual case is that this isn't required;
+ * instead, the caller can just increase the page refcount
+ * and re-use the pte the traditional way.
+ *
+ * And if we need a pre-allocated page but don't yet have
+ * one, return a negative error to let the preallocation
+ * code know so that it can do so outside the page table
+ * lock.
+ */
+static inline int
+copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+		  pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
+		  struct folio **prealloc, struct page *page)
+{
+	struct folio *new_folio;
+	pte_t pte;
+
+	new_folio = *prealloc;
+	if (!new_folio)
+		return -EAGAIN;
+
+	/*
+	 * We have a prealloc page, all good!  Take it
+	 * over and copy the page & arm it.
+	 */
+
+	if (copy_mc_user_highpage(&new_folio->page, page, addr, src_vma))
+		return -EHWPOISON;
+
+	*prealloc = NULL;
+	__folio_mark_uptodate(new_folio);
+	folio_add_new_anon_rmap(new_folio, dst_vma, addr, RMAP_EXCLUSIVE);
+	folio_add_lru_vma(new_folio, dst_vma);
+	rss[MM_ANONPAGES]++;
+
+	/* All done, just insert the new page copy in the child */
+	pte = folio_mk_pte(new_folio, dst_vma->vm_page_prot);
+	pte = maybe_mkwrite(pte_mkdirty(pte), dst_vma);
+	if (userfaultfd_protected(dst_vma) && pte_uffd(ptep_get(src_pte))) {
+		/* The uffd bit needs to be delivered to the dest pte as well */
+		pte = pte_mkuffd(pte);
+		/* Restore PAGE_NONE so the RWP marker keeps trapping */
+		if (userfaultfd_rwp(dst_vma))
+			pte = pte_modify(pte, PAGE_NONE);
+	}
+	set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
+	return 0;
+}
+
+static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma,
+		struct vm_area_struct *src_vma, pte_t *dst_pte, pte_t *src_pte,
+		pte_t pte, unsigned long addr, int nr)
+{
+	struct mm_struct *src_mm = src_vma->vm_mm;
+	bool writable;
+
+	/*
+	 * Snapshot writability before the RWP-disarm rewrite below: when the
+	 * child is not RWP-armed, pte_modify(pte, dst_vma->vm_page_prot) can
+	 * silently drop _PAGE_RW from a resolved (no-marker) writable PTE,
+	 * so a later pte_write(pte) check would skip the COW wrprotect and
+	 * leave the parent writable over a folio shared with the child.
+	 */
+	writable = pte_write(pte);
+
+	/*
+	 * Child is not RWP-armed: restore accessible protection so the
+	 * inherited PAGE_NONE does not cost a fault on first read. Gate on
+	 * pte_uffd(pte) so unrelated PAGE_NONE markers (e.g. NUMA balancing)
+	 * are not normalised away.
+	 */
+	if (!userfaultfd_protected(dst_vma)) {
+		if (userfaultfd_rwp(src_vma) && pte_uffd(pte))
+			pte = pte_modify(pte, dst_vma->vm_page_prot);
+		pte = pte_clear_uffd(pte);
+	}
+
+	/* If it's a COW mapping, write protect it both processes. */
+	if (is_cow_mapping(src_vma->vm_flags) && writable) {
+		wrprotect_ptes(src_mm, addr, src_pte, nr);
+		pte = pte_wrprotect(pte);
+	}
+
+	/* If it's a shared mapping, mark it clean in the child. */
+	if (src_vma->vm_flags & VM_SHARED)
+		pte = pte_mkclean(pte);
+	pte = pte_mkold(pte);
+
+	set_ptes(dst_vma->vm_mm, addr, dst_pte, pte, nr);
+}
+
+/*
+ * Copy one present PTE, trying to batch-process subsequent PTEs that map
+ * consecutive pages of the same folio by copying them as well.
+ *
+ * Returns -EAGAIN if one preallocated page is required to copy the next PTE.
+ * Otherwise, returns the number of copied PTEs (at least 1).
+ */
+static inline int
+copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+		 pte_t *dst_pte, pte_t *src_pte, pte_t pte, unsigned long addr,
+		 int max_nr, int *rss, struct folio **prealloc)
+{
+	fpb_t flags = FPB_MERGE_WRITE;
+	struct page *page;
+	struct folio *folio;
+	int err, nr;
+
+	page = vm_normal_page(src_vma, addr, pte);
+	if (unlikely(!page))
+		goto copy_pte;
+
+	folio = page_folio(page);
+
+	/*
+	 * If we likely have to copy, just don't bother with batching. Make
+	 * sure that the common "small folio" case is as fast as possible
+	 * by keeping the batching logic separate.
+	 */
+	if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) {
+		if (!(src_vma->vm_flags & VM_SHARED))
+			flags |= FPB_RESPECT_DIRTY;
+		if (vma_soft_dirty_enabled(src_vma))
+			flags |= FPB_RESPECT_SOFT_DIRTY;
+
+		nr = folio_pte_batch_flags(folio, src_vma, src_pte, &pte, max_nr, flags);
+		folio_ref_add(folio, nr);
+		if (folio_test_anon(folio)) {
+			if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,
+								  nr, dst_vma, src_vma))) {
+				folio_ref_sub(folio, nr);
+				return -EAGAIN;
+			}
+			rss[MM_ANONPAGES] += nr;
+			VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
+		} else {
+			folio_dup_file_rmap_ptes(folio, page, nr, dst_vma);
+			rss[mm_counter_file(folio)] += nr;
+		}
+		__copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte,
+				    addr, nr);
+		return nr;
+	}
+
+	folio_get(folio);
+	if (folio_test_anon(folio)) {
+		/*
+		 * If this page may have been pinned by the parent process,
+		 * copy the page immediately for the child so that we'll always
+		 * guarantee the pinned page won't be randomly replaced in the
+		 * future.
+		 */
+		if (unlikely(folio_try_dup_anon_rmap_pte(folio, page, dst_vma, src_vma))) {
+			/* Page may be pinned, we have to copy. */
+			folio_put(folio);
+			err = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
+						addr, rss, prealloc, page);
+			return err ? err : 1;
+		}
+		rss[MM_ANONPAGES]++;
+		VM_WARN_ON_FOLIO(PageAnonExclusive(page), folio);
+	} else {
+		folio_dup_file_rmap_pte(folio, page, dst_vma);
+		rss[mm_counter_file(folio)]++;
+	}
+
+copy_pte:
+	__copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, addr, 1);
+	return 1;
+}
+
+static inline struct folio *folio_prealloc(struct mm_struct *src_mm,
+		struct vm_area_struct *vma, unsigned long addr, bool need_zero)
+{
+	struct folio *new_folio;
+
+	if (need_zero)
+		new_folio = vma_alloc_zeroed_movable_folio(vma, addr);
+	else
+		new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr);
+
+	if (!new_folio)
+		return NULL;
+
+	if (mem_cgroup_charge(new_folio, src_mm, GFP_KERNEL)) {
+		folio_put(new_folio);
+		return NULL;
+	}
+	folio_throttle_swaprate(new_folio, GFP_KERNEL);
+
+	return new_folio;
+}
+
+static int
+copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+	       pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
+	       unsigned long end)
+{
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	struct mm_struct *src_mm = src_vma->vm_mm;
+	pte_t *orig_src_pte, *orig_dst_pte;
+	pte_t *src_pte, *dst_pte;
+	pmd_t dummy_pmdval;
+	pte_t ptent;
+	spinlock_t *src_ptl, *dst_ptl;
+	int progress, max_nr, ret = 0;
+	int rss[NR_MM_COUNTERS];
+	softleaf_t entry = softleaf_mk_none();
+	struct folio *prealloc = NULL;
+	int nr;
+
+again:
+	progress = 0;
+	init_rss_vec(rss);
+
+	/*
+	 * copy_pmd_range()'s prior pmd_none_or_clear_bad(src_pmd), and the
+	 * error handling here, assume that exclusive mmap_lock on dst and src
+	 * protects anon from unexpected THP transitions; with shmem and file
+	 * protected by mmap_lock-less collapse skipping areas with anon_vma
+	 * (whereas vma_needs_copy() skips areas without anon_vma).  A rework
+	 * can remove such assumptions later, but this is good enough for now.
+	 */
+	dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
+	if (!dst_pte) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	/*
+	 * We already hold the exclusive mmap_lock, the copy_pte_range() and
+	 * retract_page_tables() are using vma->anon_vma to be exclusive, so
+	 * the PTE page is stable, and there is no need to get pmdval and do
+	 * pmd_same() check.
+	 */
+	src_pte = pte_offset_map_rw_nolock(src_mm, src_pmd, addr, &dummy_pmdval,
+					   &src_ptl);
+	if (!src_pte) {
+		pte_unmap_unlock(dst_pte, dst_ptl);
+		/* ret == 0 */
+		goto out;
+	}
+	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
+	orig_src_pte = src_pte;
+	orig_dst_pte = dst_pte;
+	lazy_mmu_mode_enable();
+
+	do {
+		nr = 1;
+
+		/*
+		 * We are holding two locks at this point - either of them
+		 * could generate latencies in another task on another CPU.
+		 */
+		if (progress >= 32) {
+			progress = 0;
+			if (need_resched() ||
+			    spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
+				break;
+		}
+		ptent = ptep_get(src_pte);
+		if (pte_none(ptent)) {
+			progress++;
+			continue;
+		}
+		if (unlikely(!pte_present(ptent))) {
+			ret = copy_nonpresent_pte(dst_mm, src_mm,
+						  dst_pte, src_pte,
+						  dst_vma, src_vma,
+						  addr, rss);
+			if (ret == -EIO) {
+				entry = softleaf_from_pte(ptep_get(src_pte));
+				break;
+			} else if (ret == -EBUSY) {
+				break;
+			} else if (!ret) {
+				progress += 8;
+				continue;
+			}
+			ptent = ptep_get(src_pte);
+			VM_WARN_ON_ONCE(!pte_present(ptent));
+
+			/*
+			 * Device exclusive entry restored, continue by copying
+			 * the now present pte.
+			 */
+			WARN_ON_ONCE(ret != -ENOENT);
+		}
+		/* copy_present_ptes() will clear `*prealloc' if consumed */
+		max_nr = (end - addr) / PAGE_SIZE;
+		ret = copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte,
+					ptent, addr, max_nr, rss, &prealloc);
+		/*
+		 * If we need a pre-allocated page for this pte, drop the
+		 * locks, allocate, and try again.
+		 * If copy failed due to hwpoison in source page, break out.
+		 */
+		if (unlikely(ret == -EAGAIN || ret == -EHWPOISON))
+			break;
+		if (unlikely(prealloc)) {
+			/*
+			 * pre-alloc page cannot be reused by next time so as
+			 * to strictly follow mempolicy (e.g., alloc_page_vma()
+			 * will allocate page according to address).  This
+			 * could only happen if one pinned pte changed.
+			 */
+			folio_put(prealloc);
+			prealloc = NULL;
+		}
+		nr = ret;
+		progress += 8 * nr;
+	} while (dst_pte += nr, src_pte += nr, addr += PAGE_SIZE * nr,
+		 addr != end);
+
+	lazy_mmu_mode_disable();
+	pte_unmap_unlock(orig_src_pte, src_ptl);
+	add_mm_rss_vec(dst_mm, rss);
+	pte_unmap_unlock(orig_dst_pte, dst_ptl);
+	cond_resched();
+
+	if (ret == -EIO) {
+		VM_WARN_ON_ONCE(!entry.val);
+		if (swap_retry_table_alloc(entry, GFP_KERNEL) < 0) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		entry.val = 0;
+	} else if (ret == -EBUSY || unlikely(ret == -EHWPOISON)) {
+		goto out;
+	} else if (ret ==  -EAGAIN) {
+		prealloc = folio_prealloc(src_mm, src_vma, addr, false);
+		if (!prealloc)
+			return -ENOMEM;
+	} else if (ret < 0) {
+		VM_WARN_ON_ONCE(1);
+	}
+
+	/* We've captured and resolved the error. Reset, try again. */
+	ret = 0;
+
+	if (addr != end)
+		goto again;
+out:
+	if (unlikely(prealloc))
+		folio_put(prealloc);
+	return ret;
+}
+
+static inline int
+copy_pmd_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+	       pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
+	       unsigned long end)
+{
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	struct mm_struct *src_mm = src_vma->vm_mm;
+	pmd_t *src_pmd, *dst_pmd;
+	unsigned long next;
+
+	dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
+	if (!dst_pmd)
+		return -ENOMEM;
+	src_pmd = pmd_offset(src_pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_is_huge(*src_pmd)) {
+			int err;
+
+			VM_BUG_ON_VMA(next-addr != HPAGE_PMD_SIZE, src_vma);
+			err = copy_huge_pmd(dst_mm, src_mm, dst_pmd, src_pmd,
+					    addr, dst_vma, src_vma);
+			if (err == -ENOMEM)
+				return -ENOMEM;
+			if (!err)
+				continue;
+			/* fall through */
+		}
+		if (pmd_none_or_clear_bad(src_pmd))
+			continue;
+		if (copy_pte_range(dst_vma, src_vma, dst_pmd, src_pmd,
+				   addr, next))
+			return -ENOMEM;
+	} while (dst_pmd++, src_pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int
+copy_pud_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+	       p4d_t *dst_p4d, p4d_t *src_p4d, unsigned long addr,
+	       unsigned long end)
+{
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	struct mm_struct *src_mm = src_vma->vm_mm;
+	pud_t *src_pud, *dst_pud;
+	unsigned long next;
+
+	dst_pud = pud_alloc(dst_mm, dst_p4d, addr);
+	if (!dst_pud)
+		return -ENOMEM;
+	src_pud = pud_offset(src_p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_trans_huge(*src_pud)) {
+			int err;
+
+			VM_BUG_ON_VMA(next-addr != HPAGE_PUD_SIZE, src_vma);
+			err = copy_huge_pud(dst_mm, src_mm,
+					    dst_pud, src_pud, addr, src_vma);
+			if (err == -ENOMEM)
+				return -ENOMEM;
+			if (!err)
+				continue;
+			/* fall through */
+		}
+		if (pud_none_or_clear_bad(src_pud))
+			continue;
+		if (copy_pmd_range(dst_vma, src_vma, dst_pud, src_pud,
+				   addr, next))
+			return -ENOMEM;
+	} while (dst_pud++, src_pud++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int
+copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+	       pgd_t *dst_pgd, pgd_t *src_pgd, unsigned long addr,
+	       unsigned long end)
+{
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	p4d_t *src_p4d, *dst_p4d;
+	unsigned long next;
+
+	dst_p4d = p4d_alloc(dst_mm, dst_pgd, addr);
+	if (!dst_p4d)
+		return -ENOMEM;
+	src_p4d = p4d_offset(src_pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(src_p4d))
+			continue;
+		if (copy_pud_range(dst_vma, src_vma, dst_p4d, src_p4d,
+				   addr, next))
+			return -ENOMEM;
+	} while (dst_p4d++, src_p4d++, addr = next, addr != end);
+	return 0;
+}
+
+/*
+ * Return true if the vma needs to copy the pgtable during this fork().  Return
+ * false when we can speed up fork() by allowing lazy page faults later until
+ * when the child accesses the memory range.
+ */
+static bool
+vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
+{
+	/*
+	 * We check against dst_vma as while sane VMA flags will have been
+	 * copied, VM_UFFD_WP may be set only on dst_vma.
+	 */
+	if (dst_vma->vm_flags & VM_COPY_ON_FORK)
+		return true;
+	/*
+	 * The presence of an anon_vma indicates an anonymous VMA has page
+	 * tables which naturally cannot be reconstituted on page fault.
+	 */
+	if (src_vma->anon_vma)
+		return true;
+
+	/*
+	 * Don't copy ptes where a page fault will fill them correctly.  Fork
+	 * becomes much lighter when there are big shared or private readonly
+	 * mappings. The tradeoff is that copy_page_range is more efficient
+	 * than faulting.
+	 */
+	return false;
+}
+
+int
+copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
+{
+	pgd_t *src_pgd, *dst_pgd;
+	unsigned long addr = src_vma->vm_start;
+	unsigned long end = src_vma->vm_end;
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	struct mm_struct *src_mm = src_vma->vm_mm;
+	struct mmu_notifier_range range;
+	unsigned long next;
+	bool is_cow;
+	int ret;
+
+	if (!vma_needs_copy(dst_vma, src_vma))
+		return 0;
+
+	if (is_vm_hugetlb_page(src_vma))
+		return copy_hugetlb_page_range(dst_mm, src_mm, dst_vma, src_vma);
+
+	/*
+	 * We need to invalidate the secondary MMU mappings only when
+	 * there could be a permission downgrade on the ptes of the
+	 * parent mm. And a permission downgrade will only happen if
+	 * is_cow_mapping() returns true.
+	 */
+	is_cow = is_cow_mapping(src_vma->vm_flags);
+
+	if (is_cow) {
+		mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
+					0, src_mm, addr, end);
+		mmu_notifier_invalidate_range_start(&range);
+		/*
+		 * Disabling preemption is not needed for the write side, as
+		 * the read side doesn't spin, but goes to the mmap_lock.
+		 *
+		 * Use the raw variant of the seqcount_t write API to avoid
+		 * lockdep complaining about preemptibility.
+		 */
+		vma_assert_write_locked(src_vma);
+		raw_write_seqcount_begin(&src_mm->write_protect_seq);
+	}
+
+	ret = 0;
+	dst_pgd = pgd_offset(dst_mm, addr);
+	src_pgd = pgd_offset(src_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(src_pgd))
+			continue;
+		if (unlikely(copy_p4d_range(dst_vma, src_vma, dst_pgd, src_pgd,
+					    addr, next))) {
+			ret = -ENOMEM;
+			break;
+		}
+	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
+
+	if (is_cow) {
+		raw_write_seqcount_end(&src_mm->write_protect_seq);
+		mmu_notifier_invalidate_range_end(&range);
+	}
+	return ret;
+}
+
+/* Whether we should zap all COWed (private) pages too */
+static inline bool should_zap_cows(struct zap_details *details)
+{
+	/* By default, zap all pages */
+	if (!details)
+		return true;
+
+	VM_WARN_ON_ONCE(details->skip_cows && details->reclaim_pt);
+
+	/* Or, we zap COWed pages only if the caller wants to */
+	return !details->skip_cows;
+}
+
+/* Decides whether we should zap this folio with the folio pointer specified */
+static inline bool should_zap_folio(struct zap_details *details,
+				    struct folio *folio)
+{
+	/* If we can make a decision without *folio.. */
+	if (should_zap_cows(details))
+		return true;
+
+	/* Otherwise we should only zap non-anon folios */
+	return !folio_test_anon(folio);
+}
+
+static inline bool zap_drop_markers(struct zap_details *details)
+{
+	if (!details)
+		return false;
+
+	return details->zap_flags & ZAP_FLAG_DROP_MARKER;
+}
+
+/**
+ * cond_install_uffd_wp_ptes - install uffd-wp markers after clearing PTEs
+ * @vma: The VMA the pages are mapped into.
+ * @addr: Address the first page of this batch is mapped at.
+ * @ptep: Page table pointer for the first entry of this batch.
+ * @pte: Old value of the entry pointed to by @ptep.
+ * @nr_ptes: Number of entries to install.
+ *
+ * If the PTEs were write-protected by uffd-wp in any form, arm special PTEs
+ * to replace none PTEs. NOTE! This should only be called when the PTEs are
+ * already cleared so we will never accidentally replace something valuable.
+ * Meanwhile none PTEs also mean we are not demoting the PTEs so a TLB flush is
+ * not needed. E.g., when the PTEs were cleared, the caller should have taken
+ * care of the TLB flush.
+ *
+ * Must be called with the page table lock held so that no thread will see the
+ * none PTEs, and if they see them, they'll fault and serialize at the page table
+ * lock.
+ *
+ * Returns true if uffd-wp PTEs were installed, false otherwise.
+ */
+bool cond_install_uffd_wp_ptes(struct vm_area_struct *vma,
+		unsigned long addr, pte_t *ptep, pte_t pte,
+		unsigned long nr_ptes)
+{
+	bool arm_uffd_pte = false;
+
+	if (!uffd_supports_wp_marker())
+		return false;
+
+	/* The current status of the pte should be "cleared" before calling */
+	WARN_ON_ONCE(!pte_none(ptep_get(ptep)));
+
+	/*
+	 * NOTE: userfaultfd_wp_unpopulated() doesn't need this whole
+	 * thing, because when zapping either it means it's dropping the
+	 * page, or in TTU where the present pte will be quickly replaced
+	 * with a swap pte.  There's no way of leaking the bit.
+	 */
+	if (vma_is_anonymous(vma) || !userfaultfd_wp(vma))
+		return false;
+
+	/* A uffd-wp wr-protected normal pte */
+	if (unlikely(pte_present(pte) && pte_uffd(pte)))
+		arm_uffd_pte = true;
+
+	/*
+	 * A uffd-wp wr-protected swap pte.  Note: this should even cover an
+	 * existing pte marker with uffd-wp bit set.
+	 */
+	if (unlikely(pte_swp_uffd_any(pte)))
+		arm_uffd_pte = true;
+
+	if (likely(!arm_uffd_pte))
+		return false;
+
+	for (;;) {
+		set_pte_at(vma->vm_mm, addr, ptep,
+			   make_pte_marker(PTE_MARKER_UFFD_WP));
+		if (--nr_ptes == 0)
+			break;
+		ptep++;
+		addr += PAGE_SIZE;
+	}
+
+	return true;
+}
+
+/*
+ * This function makes sure that we'll replace the none pte with an uffd-wp
+ * swap special pte marker when necessary. Must be with the pgtable lock held.
+ *
+ * Returns true if uffd-wp ptes was installed, false otherwise.
+ */
+static inline bool
+zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
+			      unsigned long addr, pte_t *pte, int nr,
+			      struct zap_details *details, pte_t pteval)
+{
+	if (zap_drop_markers(details))
+		return false;
+
+	return cond_install_uffd_wp_ptes(vma, addr, pte, pteval, nr);
+}
+
+static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, struct folio *folio,
+		struct page *page, pte_t *pte, pte_t ptent, unsigned int nr,
+		unsigned long addr, struct zap_details *details, int *rss,
+		bool *force_flush, bool *force_break, bool *any_skipped)
+{
+	struct mm_struct *mm = tlb->mm;
+	bool delay_rmap = false;
+
+	if (!folio_test_anon(folio)) {
+		ptent = get_and_clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
+		if (pte_dirty(ptent)) {
+			folio_mark_dirty(folio);
+			if (tlb_delay_rmap(tlb)) {
+				delay_rmap = true;
+				*force_flush = true;
+			}
+		}
+		if (pte_young(ptent) && likely(vma_has_recency(vma)))
+			folio_mark_accessed(folio);
+		rss[mm_counter(folio)] -= nr;
+	} else {
+		/* We don't need up-to-date accessed/dirty bits. */
+		clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
+		rss[MM_ANONPAGES] -= nr;
+	}
+	/* Checking a single PTE in a batch is sufficient. */
+	arch_check_zapped_pte(vma, ptent);
+	tlb_remove_tlb_entries(tlb, pte, nr, addr);
+	if (unlikely(userfaultfd_pte_wp(vma, ptent)))
+		*any_skipped = zap_install_uffd_wp_if_needed(vma, addr, pte,
+							     nr, details, ptent);
+
+	if (!delay_rmap) {
+		folio_remove_rmap_ptes(folio, page, nr, vma);
+
+		if (unlikely(folio_mapcount(folio) < 0))
+			print_bad_pte(vma, addr, ptent, page);
+	}
+	if (unlikely(__tlb_remove_folio_pages(tlb, page, nr, delay_rmap))) {
+		*force_flush = true;
+		*force_break = true;
+	}
+}
+
+/*
+ * Zap or skip at least one present PTE, trying to batch-process subsequent
+ * PTEs that map consecutive pages of the same folio.
+ *
+ * Returns the number of processed (skipped or zapped) PTEs (at least 1).
+ */
+static inline int zap_present_ptes(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
+		unsigned int max_nr, unsigned long addr,
+		struct zap_details *details, int *rss, bool *force_flush,
+		bool *force_break, bool *any_skipped)
+{
+	struct mm_struct *mm = tlb->mm;
+	struct folio *folio;
+	struct page *page;
+	int nr;
+
+	page = vm_normal_page(vma, addr, ptent);
+	if (!page) {
+		/* We don't need up-to-date accessed/dirty bits. */
+		ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
+		arch_check_zapped_pte(vma, ptent);
+		tlb_remove_tlb_entry(tlb, pte, addr);
+		if (userfaultfd_pte_wp(vma, ptent))
+			*any_skipped = zap_install_uffd_wp_if_needed(vma, addr,
+						pte, 1, details, ptent);
+		ksm_might_unmap_zero_page(mm, ptent);
+		return 1;
+	}
+
+	folio = page_folio(page);
+	if (unlikely(!should_zap_folio(details, folio))) {
+		*any_skipped = true;
+		return 1;
+	}
+
+	/*
+	 * Make sure that the common "small folio" case is as fast as possible
+	 * by keeping the batching logic separate.
+	 */
+	if (unlikely(folio_test_large(folio) && max_nr != 1)) {
+		nr = folio_pte_batch(folio, pte, ptent, max_nr);
+		zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr,
+				       addr, details, rss, force_flush,
+				       force_break, any_skipped);
+		return nr;
+	}
+	zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, 1, addr,
+			       details, rss, force_flush, force_break, any_skipped);
+	return 1;
+}
+
+static inline int zap_nonpresent_ptes(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
+		unsigned int max_nr, unsigned long addr,
+		struct zap_details *details, int *rss, bool *any_skipped)
+{
+	softleaf_t entry;
+	int nr = 1;
+
+	*any_skipped = true;
+	entry = softleaf_from_pte(ptent);
+	if (softleaf_is_device_private(entry) ||
+	    softleaf_is_device_exclusive(entry)) {
+		struct page *page = softleaf_to_page(entry);
+		struct folio *folio = page_folio(page);
+
+		if (unlikely(!should_zap_folio(details, folio)))
+			return 1;
+		/*
+		 * Both device private/exclusive mappings should only
+		 * work with anonymous page so far, so we don't need to
+		 * consider uffd-wp bit when zap. For more information,
+		 * see zap_install_uffd_wp_if_needed().
+		 */
+		WARN_ON_ONCE(!folio_test_anon(folio));
+		rss[mm_counter(folio)]--;
+		folio_remove_rmap_pte(folio, page, vma);
+		folio_put(folio);
+	} else if (softleaf_is_swap(entry)) {
+		/* Genuine swap entries, hence a private anon pages */
+		if (!should_zap_cows(details))
+			return 1;
+
+		nr = swap_pte_batch(pte, max_nr, ptent);
+		rss[MM_SWAPENTS] -= nr;
+		swap_put_entries_direct(entry, nr);
+	} else if (softleaf_is_migration(entry)) {
+		struct folio *folio = softleaf_to_folio(entry);
+
+		if (!should_zap_folio(details, folio))
+			return 1;
+		rss[mm_counter(folio)]--;
+	} else if (softleaf_is_uffd_wp_marker(entry)) {
+		/*
+		 * For anon: always drop the marker; for file: only
+		 * drop the marker if explicitly requested.
+		 */
+		if (!vma_is_anonymous(vma) && !zap_drop_markers(details))
+			return 1;
+	} else if (softleaf_is_guard_marker(entry)) {
+		/*
+		 * Ordinary zapping should not remove guard PTE
+		 * markers. Only do so if we should remove PTE markers
+		 * in general.
+		 */
+		if (!zap_drop_markers(details))
+			return 1;
+	} else if (softleaf_is_hwpoison(entry) ||
+		   softleaf_is_poison_marker(entry)) {
+		if (!should_zap_cows(details))
+			return 1;
+	} else {
+		/* We should have covered all the swap entry types */
+		pr_alert("unrecognized swap entry 0x%lx\n", entry.val);
+		WARN_ON_ONCE(1);
+	}
+	clear_nonpresent_ptes(vma->vm_mm, addr, pte, nr);
+	*any_skipped = zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent);
+
+	return nr;
+}
+
+static inline int do_zap_pte_range(struct mmu_gather *tlb,
+				   struct vm_area_struct *vma, pte_t *pte,
+				   unsigned long addr, unsigned long end,
+				   struct zap_details *details, int *rss,
+				   bool *force_flush, bool *force_break,
+				   bool *any_skipped)
+{
+	pte_t ptent = ptep_get(pte);
+	int max_nr = (end - addr) / PAGE_SIZE;
+	int nr = 0;
+
+	/* Skip all consecutive none ptes */
+	if (pte_none(ptent)) {
+		for (nr = 1; nr < max_nr; nr++) {
+			ptent = ptep_get(pte + nr);
+			if (!pte_none(ptent))
+				break;
+		}
+		max_nr -= nr;
+		if (!max_nr)
+			return nr;
+		pte += nr;
+		addr += nr * PAGE_SIZE;
+	}
+
+	if (pte_present(ptent))
+		nr += zap_present_ptes(tlb, vma, pte, ptent, max_nr, addr,
+				       details, rss, force_flush, force_break,
+				       any_skipped);
+	else
+		nr += zap_nonpresent_ptes(tlb, vma, pte, ptent, max_nr, addr,
+					  details, rss, any_skipped);
+
+	return nr;
+}
+
+static bool pte_table_reclaim_possible(unsigned long start, unsigned long end,
+		struct zap_details *details)
+{
+	if (!IS_ENABLED(CONFIG_PT_RECLAIM))
+		return false;
+	/* Only zap if we are allowed to and cover the full page table. */
+	return details && details->reclaim_pt && (end - start >= PMD_SIZE);
+}
+
+static bool zap_empty_pte_table(struct mm_struct *mm, pmd_t *pmd,
+		spinlock_t *ptl, pmd_t *pmdval)
+{
+	spinlock_t *pml = pmd_lockptr(mm, pmd);
+
+	if (ptl != pml && !spin_trylock(pml))
+		return false;
+
+	*pmdval = pmdp_get(pmd);
+	pmd_clear(pmd);
+	if (ptl != pml)
+		spin_unlock(pml);
+	return true;
+}
+
+static bool zap_pte_table_if_empty(struct mm_struct *mm, pmd_t *pmd,
+		unsigned long addr, pmd_t *pmdval)
+{
+	spinlock_t *pml, *ptl = NULL;
+	pte_t *start_pte, *pte;
+	int i;
+
+	pml = pmd_lock(mm, pmd);
+	start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, pmdval, &ptl);
+	if (!start_pte)
+		goto out_ptl;
+	if (ptl != pml)
+		spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+
+	for (i = 0, pte = start_pte; i < PTRS_PER_PTE; i++, pte++) {
+		if (!pte_none(ptep_get(pte)))
+			goto out_ptl;
+	}
+	pte_unmap(start_pte);
+
+	pmd_clear(pmd);
+
+	if (ptl != pml)
+		spin_unlock(ptl);
+	spin_unlock(pml);
+	return true;
+out_ptl:
+	if (start_pte)
+		pte_unmap_unlock(start_pte, ptl);
+	if (ptl != pml)
+		spin_unlock(pml);
+	return false;
+}
+
+static unsigned long zap_pte_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pmd_t *pmd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	bool can_reclaim_pt = pte_table_reclaim_possible(addr, end, details);
+	bool force_flush = false, force_break = false;
+	struct mm_struct *mm = tlb->mm;
+	int rss[NR_MM_COUNTERS];
+	spinlock_t *ptl;
+	pte_t *start_pte;
+	pte_t *pte;
+	pmd_t pmdval;
+	unsigned long start = addr;
+	bool direct_reclaim = true;
+	int nr;
+
+retry:
+	tlb_change_page_size(tlb, PAGE_SIZE);
+	init_rss_vec(rss);
+	start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+	if (!pte)
+		return addr;
+
+	flush_tlb_batched_pending(mm);
+	lazy_mmu_mode_enable();
+	do {
+		bool any_skipped = false;
+
+		if (need_resched()) {
+			direct_reclaim = false;
+			break;
+		}
+
+		nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, rss,
+				      &force_flush, &force_break, &any_skipped);
+		if (any_skipped)
+			can_reclaim_pt = false;
+		if (unlikely(force_break)) {
+			addr += nr * PAGE_SIZE;
+			direct_reclaim = false;
+			break;
+		}
+	} while (pte += nr, addr += PAGE_SIZE * nr, addr != end);
+
+	/*
+	 * Fast path: try to hold the pmd lock and unmap the PTE page.
+	 *
+	 * If the pte lock was released midway (retry case), or if the attempt
+	 * to hold the pmd lock failed, then we need to recheck all pte entries
+	 * to ensure they are still none, thereby preventing the pte entries
+	 * from being repopulated by another thread.
+	 */
+	if (can_reclaim_pt && direct_reclaim && addr == end)
+		direct_reclaim = zap_empty_pte_table(mm, pmd, ptl, &pmdval);
+
+	add_mm_rss_vec(mm, rss);
+	lazy_mmu_mode_disable();
+
+	/* Do the actual TLB flush before dropping ptl */
+	if (force_flush) {
+		tlb_flush_mmu_tlbonly(tlb);
+		tlb_flush_rmaps(tlb, vma);
+	}
+	pte_unmap_unlock(start_pte, ptl);
+
+	/*
+	 * If we forced a TLB flush (either due to running out of
+	 * batch buffers or because we needed to flush dirty TLB
+	 * entries before releasing the ptl), free the batched
+	 * memory too. Come back again if we didn't do everything.
+	 */
+	if (force_flush)
+		tlb_flush_mmu(tlb);
+
+	if (addr != end) {
+		cond_resched();
+		force_flush = false;
+		force_break = false;
+		goto retry;
+	}
+
+	if (can_reclaim_pt) {
+		if (direct_reclaim || zap_pte_table_if_empty(mm, pmd, start, &pmdval)) {
+			pte_free_tlb(tlb, pmd_pgtable(pmdval), start);
+			mm_dec_nr_ptes(mm);
+		}
+	}
+
+	return addr;
+}
+
+static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_is_huge(*pmd)) {
+			if (next - addr != HPAGE_PMD_SIZE)
+				__split_huge_pmd(vma, pmd, addr, false);
+			else if (zap_huge_pmd(tlb, vma, pmd, addr)) {
+				addr = next;
+				continue;
+			}
+			/* fall through */
+		} else if (details && details->single_folio &&
+			   folio_test_pmd_mappable(details->single_folio) &&
+			   next - addr == HPAGE_PMD_SIZE && pmd_none(*pmd)) {
+			sync_with_folio_pmd_zap(tlb->mm, pmd);
+		}
+		if (pmd_none(*pmd)) {
+			addr = next;
+			continue;
+		}
+		addr = zap_pte_range(tlb, vma, pmd, addr, next, details);
+		if (addr != next)
+			pmd--;
+	} while (pmd++, cond_resched(), addr != end);
+
+	return addr;
+}
+
+static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_trans_huge(*pud)) {
+			if (next - addr != HPAGE_PUD_SIZE)
+				split_huge_pud(vma, pud, addr);
+			else if (zap_huge_pud(tlb, vma, pud, addr))
+				goto next;
+			/* fall through */
+		}
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		next = zap_pmd_range(tlb, vma, pud, addr, next, details);
+next:
+		cond_resched();
+	} while (pud++, addr = next, addr != end);
+
+	return addr;
+}
+
+static inline unsigned long zap_p4d_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	p4d_t *p4d;
+	unsigned long next;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		next = zap_pud_range(tlb, vma, p4d, addr, next, details);
+	} while (p4d++, addr = next, addr != end);
+
+	return addr;
+}
+
+static void __zap_vma_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		struct zap_details *details)
+{
+	const bool reaping = details && details->reaping;
+
+	VM_WARN_ON_ONCE(start >= end || !range_in_vma(vma, start, end));
+
+	/* uprobe_munmap() might sleep, so skip it when reaping. */
+	if (vma->vm_file && !reaping)
+		uprobe_munmap(vma, start, end);
+
+	if (unlikely(is_vm_hugetlb_page(vma))) {
+		zap_flags_t zap_flags = details ? details->zap_flags : 0;
+
+		VM_WARN_ON_ONCE(reaping);
+		/*
+		 * vm_file will be NULL when we fail early while instantiating
+		 * a new mapping. In this case, no pages were mapped yet and
+		 * there is nothing to do.
+		 */
+		if (!vma->vm_file)
+			return;
+		__unmap_hugepage_range(tlb, vma, start, end, NULL, zap_flags);
+	} else {
+		unsigned long next, addr = start;
+		pgd_t *pgd;
+
+		tlb_start_vma(tlb, vma);
+		pgd = pgd_offset(vma->vm_mm, addr);
+		do {
+			next = pgd_addr_end(addr, end);
+			if (pgd_none_or_clear_bad(pgd))
+				continue;
+			next = zap_p4d_range(tlb, vma, pgd, addr, next, details);
+		} while (pgd++, addr = next, addr != end);
+		tlb_end_vma(tlb, vma);
+	}
+}
+
+/**
+ * zap_vma_for_reaping - zap all page table entries in the vma without blocking
+ * @vma: The vma to zap.
+ *
+ * Zap all page table entries in the vma without blocking for use by the oom
+ * killer. Hugetlb vmas are not supported.
+ *
+ * Returns: 0 on success, -EBUSY if we would have to block.
+ */
+int zap_vma_for_reaping(struct vm_area_struct *vma)
+{
+	struct zap_details details = {
+		.reaping = true,
+	};
+	struct mmu_notifier_range range;
+	struct mmu_gather tlb;
+
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
+				vma->vm_start, vma->vm_end);
+	tlb_gather_mmu(&tlb, vma->vm_mm);
+	if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
+		tlb_finish_mmu(&tlb);
+		return -EBUSY;
+	}
+	__zap_vma_range(&tlb, vma, range.start, range.end, &details);
+	mmu_notifier_invalidate_range_end(&range);
+	tlb_finish_mmu(&tlb);
+	return 0;
+}
+
+/**
+ * unmap_vmas - unmap a range of memory covered by a list of vma's
+ * @tlb: address of the caller's struct mmu_gather
+ * @unmap: The unmap_desc
+ *
+ * Unmap all pages in the vma list.
+ *
+ * Only addresses between `start' and `end' will be unmapped.
+ *
+ * The VMA list must be sorted in ascending virtual address order.
+ *
+ * unmap_vmas() assumes that the caller will flush the whole unmapped address
+ * range after unmap_vmas() returns.  So the only responsibility here is to
+ * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
+ * drops the lock and schedules.
+ */
+void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap)
+{
+	struct vm_area_struct *vma;
+	struct mmu_notifier_range range;
+	struct zap_details details = {
+		.zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP,
+	};
+
+	vma = unmap->first;
+	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma->vm_mm,
+				unmap->vma_start, unmap->vma_end);
+	mmu_notifier_invalidate_range_start(&range);
+	do {
+		unsigned long start = max(vma->vm_start, unmap->vma_start);
+		unsigned long end = min(vma->vm_end, unmap->vma_end);
+
+		hugetlb_zap_begin(vma, &start, &end);
+		__zap_vma_range(tlb, vma, start, end, &details);
+		hugetlb_zap_end(vma, &details);
+		vma = mas_find(unmap->mas, unmap->tree_end - 1);
+	} while (vma);
+	mmu_notifier_invalidate_range_end(&range);
+}
+
+/**
+ * zap_vma_range_batched - zap page table entries in a vma range
+ * @tlb: pointer to the caller's struct mmu_gather
+ * @vma: the vma covering the range to zap
+ * @address: starting address of the range to zap
+ * @size: number of bytes to zap
+ * @details: details specifying zapping behavior
+ *
+ * @tlb must not be NULL. The provided address range must be fully
+ * contained within @vma. If @vma is for hugetlb, @tlb is flushed and
+ * re-initialized by this function.
+ *
+ * If @details is NULL, this function will zap all page table entries.
+ */
+void zap_vma_range_batched(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, unsigned long address,
+		unsigned long size, struct zap_details *details)
+{
+	const unsigned long end = address + size;
+	struct mmu_notifier_range range;
+
+	VM_WARN_ON_ONCE(!tlb || tlb->mm != vma->vm_mm);
+
+	if (unlikely(!size))
+		return;
+
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
+				address, end);
+	hugetlb_zap_begin(vma, &range.start, &range.end);
+	update_hiwater_rss(vma->vm_mm);
+	mmu_notifier_invalidate_range_start(&range);
+	/*
+	 * unmap 'address-end' not 'range.start-range.end' as range
+	 * could have been expanded for hugetlb pmd sharing.
+	 */
+	__zap_vma_range(tlb, vma, address, end, details);
+	mmu_notifier_invalidate_range_end(&range);
+	if (is_vm_hugetlb_page(vma)) {
+		/*
+		 * flush tlb and free resources before hugetlb_zap_end(), to
+		 * avoid concurrent page faults' allocation failure.
+		 */
+		tlb_finish_mmu(tlb);
+		hugetlb_zap_end(vma, details);
+		tlb_gather_mmu(tlb, vma->vm_mm);
+	}
+}
+
+/**
+ * zap_vma_range - zap all page table entries in a vma range
+ * @vma: the vma covering the range to zap
+ * @address: starting address of the range to zap
+ * @size: number of bytes to zap
+ *
+ * The provided address range must be fully contained within @vma.
+ */
+void zap_vma_range(struct vm_area_struct *vma, unsigned long address,
+		unsigned long size)
+{
+	struct mmu_gather tlb;
+
+	tlb_gather_mmu(&tlb, vma->vm_mm);
+	zap_vma_range_batched(&tlb, vma, address, size, NULL);
+	tlb_finish_mmu(&tlb);
+}
+
+/**
+ * zap_special_vma_range - zap all page table entries in a special vma range
+ * @vma: the vma covering the range to zap
+ * @address: starting address of the range to zap
+ * @size: number of bytes to zap
+ *
+ * This function does nothing when the provided address range is not fully
+ * contained in @vma, or when the @vma is not VM_PFNMAP or VM_MIXEDMAP.
+ */
+void zap_special_vma_range(struct vm_area_struct *vma, unsigned long address,
+		unsigned long size)
+{
+	if (!range_in_vma(vma, address, address + size) ||
+	   !(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)))
+		return;
+
+	zap_vma_range(vma, address, size);
+}
+EXPORT_SYMBOL_GPL(zap_special_vma_range);
+
+static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pgd = pgd_offset(mm, addr);
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return NULL;
+	pud = pud_alloc(mm, p4d, addr);
+	if (!pud)
+		return NULL;
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return NULL;
+
+	VM_BUG_ON(pmd_trans_huge(*pmd));
+	return pmd;
+}
+
+pte_t *get_locked_pte(struct mm_struct *mm, unsigned long addr,
+		      spinlock_t **ptl)
+{
+	pmd_t *pmd = walk_to_pmd(mm, addr);
+
+	if (!pmd)
+		return NULL;
+	return pte_alloc_map_lock(mm, pmd, addr, ptl);
+}
+
+static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma)
+{
+	VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP);
+	/*
+	 * Whoever wants to forbid the zeropage after some zeropages
+	 * might already have been mapped has to scan the page tables and
+	 * bail out on any zeropages. Zeropages in COW mappings can
+	 * be unshared using FAULT_FLAG_UNSHARE faults.
+	 */
+	if (mm_forbids_zeropage(vma->vm_mm))
+		return false;
+	/* zeropages in COW mappings are common and unproblematic. */
+	if (is_cow_mapping(vma->vm_flags))
+		return true;
+	/* Mappings that do not allow for writable PTEs are unproblematic. */
+	if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE)))
+		return true;
+	/*
+	 * Why not allow any VMA that has vm_ops->pfn_mkwrite? GUP could
+	 * find the shared zeropage and longterm-pin it, which would
+	 * be problematic as soon as the zeropage gets replaced by a different
+	 * page due to vma->vm_ops->pfn_mkwrite, because what's mapped would
+	 * now differ to what GUP looked up. FSDAX is incompatible to
+	 * FOLL_LONGTERM and VM_IO is incompatible to GUP completely (see
+	 * check_vma_flags).
+	 */
+	return vma->vm_ops && vma->vm_ops->pfn_mkwrite &&
+	       (vma_is_fsdax(vma) || vma->vm_flags & VM_IO);
+}
+
+static int validate_page_before_insert(struct vm_area_struct *vma,
+				       struct page *page)
+{
+	struct folio *folio = page_folio(page);
+
+	if (!folio_ref_count(folio))
+		return -EINVAL;
+	if (unlikely(is_zero_folio(folio))) {
+		if (!vm_mixed_zeropage_allowed(vma))
+			return -EINVAL;
+		return 0;
+	}
+	if (folio_test_anon(folio) || page_has_type(page))
+		return -EINVAL;
+	flush_dcache_folio(folio);
+	return 0;
+}
+
+static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte,
+				unsigned long addr, struct page *page,
+				pgprot_t prot, bool mkwrite)
+{
+	struct folio *folio = page_folio(page);
+	pte_t pteval = ptep_get(pte);
+
+	if (!pte_none(pteval)) {
+		if (!mkwrite)
+			return -EBUSY;
+
+		/* see insert_pfn(). */
+		if (pte_pfn(pteval) != page_to_pfn(page)) {
+			WARN_ON_ONCE(!is_zero_pfn(pte_pfn(pteval)));
+			return -EFAULT;
+		}
+		pteval = maybe_mkwrite(pteval, vma);
+		pteval = pte_mkyoung(pteval);
+		if (ptep_set_access_flags(vma, addr, pte, pteval, 1))
+			update_mmu_cache(vma, addr, pte);
+		return 0;
+	}
+
+	/* Ok, finally just insert the thing.. */
+	pteval = mk_pte(page, prot);
+	if (unlikely(is_zero_folio(folio))) {
+		pteval = pte_mkspecial(pteval);
+	} else {
+		folio_get(folio);
+		pteval = mk_pte(page, prot);
+		if (mkwrite) {
+			pteval = pte_mkyoung(pteval);
+			pteval = maybe_mkwrite(pte_mkdirty(pteval), vma);
+		}
+		inc_mm_counter(vma->vm_mm, mm_counter_file(folio));
+		folio_add_file_rmap_pte(folio, page, vma);
+	}
+	set_pte_at(vma->vm_mm, addr, pte, pteval);
+	return 0;
+}
+
+static int insert_page(struct vm_area_struct *vma, unsigned long addr,
+			struct page *page, pgprot_t prot, bool mkwrite)
+{
+	int retval;
+	pte_t *pte;
+	spinlock_t *ptl;
+
+	retval = validate_page_before_insert(vma, page);
+	if (retval)
+		goto out;
+	retval = -ENOMEM;
+	pte = get_locked_pte(vma->vm_mm, addr, &ptl);
+	if (!pte)
+		goto out;
+	retval = insert_page_into_pte_locked(vma, pte, addr, page, prot,
+					mkwrite);
+	pte_unmap_unlock(pte, ptl);
+out:
+	return retval;
+}
+
+static int insert_page_in_batch_locked(struct vm_area_struct *vma, pte_t *pte,
+			unsigned long addr, struct page *page, pgprot_t prot)
+{
+	int err;
+
+	err = validate_page_before_insert(vma, page);
+	if (err)
+		return err;
+	return insert_page_into_pte_locked(vma, pte, addr, page, prot, false);
+}
+
+/* insert_pages() amortizes the cost of spinlock operations
+ * when inserting pages in a loop.
+ */
+static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
+			struct page **pages, unsigned long *num, pgprot_t prot)
+{
+	pmd_t *pmd = NULL;
+	pte_t *start_pte, *pte;
+	spinlock_t *pte_lock;
+	struct mm_struct *const mm = vma->vm_mm;
+	unsigned long curr_page_idx = 0;
+	unsigned long remaining_pages_total = *num;
+	unsigned long pages_to_write_in_pmd;
+	int ret;
+more:
+	ret = -EFAULT;
+	pmd = walk_to_pmd(mm, addr);
+	if (!pmd)
+		goto out;
+
+	pages_to_write_in_pmd = min_t(unsigned long,
+		remaining_pages_total, PTRS_PER_PTE - pte_index(addr));
+
+	/* Allocate the PTE if necessary; takes PMD lock once only. */
+	ret = -ENOMEM;
+	if (pte_alloc(mm, pmd))
+		goto out;
+
+	while (pages_to_write_in_pmd) {
+		int pte_idx = 0;
+		const int batch_size = min_t(int, pages_to_write_in_pmd, 8);
+
+		start_pte = pte_offset_map_lock(mm, pmd, addr, &pte_lock);
+		if (!start_pte) {
+			ret = -EFAULT;
+			goto out;
+		}
+		for (pte = start_pte; pte_idx < batch_size; ++pte, ++pte_idx) {
+			int err = insert_page_in_batch_locked(vma, pte,
+				addr, pages[curr_page_idx], prot);
+			if (unlikely(err)) {
+				pte_unmap_unlock(start_pte, pte_lock);
+				ret = err;
+				remaining_pages_total -= pte_idx;
+				goto out;
+			}
+			addr += PAGE_SIZE;
+			++curr_page_idx;
+		}
+		pte_unmap_unlock(start_pte, pte_lock);
+		pages_to_write_in_pmd -= batch_size;
+		remaining_pages_total -= batch_size;
+	}
+	if (remaining_pages_total)
+		goto more;
+	ret = 0;
+out:
+	*num = remaining_pages_total;
+	return ret;
+}
+
+/**
+ * vm_insert_pages - insert multiple pages into user vma, batching the pmd lock.
+ * @vma: user vma to map to
+ * @addr: target start user address of these pages
+ * @pages: source kernel pages
+ * @num: in: number of pages to map. out: number of pages that were *not*
+ * mapped. (0 means all pages were successfully mapped).
+ *
+ * Preferred over vm_insert_page() when inserting multiple pages.
+ *
+ * In case of error, we may have mapped a subset of the provided
+ * pages. It is the caller's responsibility to account for this case.
+ *
+ * The same restrictions apply as in vm_insert_page().
+ */
+int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
+			struct page **pages, unsigned long *num)
+{
+	const unsigned long nr_pages = *num;
+	const unsigned long end = addr + PAGE_SIZE * nr_pages;
+
+	if (!range_in_vma(vma, addr, end))
+		return -EFAULT;
+	if (!(vma->vm_flags & VM_MIXEDMAP)) {
+		VM_WARN_ON_ONCE(mmap_read_trylock(vma->vm_mm));
+		VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP);
+		vm_flags_set(vma, VM_MIXEDMAP);
+	}
+	/* Defer page refcount checking till we're about to map that page. */
+	return insert_pages(vma, addr, pages, num, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_pages);
+
+int map_kernel_pages_prepare(struct vm_area_desc *desc)
+{
+	const struct mmap_action *action = &desc->action;
+	const unsigned long addr = action->map_kernel.start;
+	unsigned long nr_pages, end;
+
+	if (!vma_desc_test(desc, VMA_MIXEDMAP_BIT)) {
+		VM_WARN_ON_ONCE(mmap_read_trylock(desc->mm));
+		VM_WARN_ON_ONCE(vma_desc_test(desc, VMA_PFNMAP_BIT));
+		vma_desc_set_flags(desc, VMA_MIXEDMAP_BIT);
+	}
+
+	nr_pages = action->map_kernel.nr_pages;
+	end = addr + PAGE_SIZE * nr_pages;
+	if (!range_in_vma_desc(desc, addr, end))
+		return -EFAULT;
+
+	return 0;
+}
+EXPORT_SYMBOL(map_kernel_pages_prepare);
+
+int map_kernel_pages_complete(struct vm_area_struct *vma,
+			      struct mmap_action *action)
+{
+	unsigned long nr_pages;
+
+	nr_pages = action->map_kernel.nr_pages;
+	return insert_pages(vma, action->map_kernel.start,
+			    action->map_kernel.pages,
+			    &nr_pages, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(map_kernel_pages_complete);
+
+/**
+ * vm_insert_page - insert single page into user vma
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @page: source kernel page
+ *
+ * This allows drivers to insert individual pages they've allocated
+ * into a user vma. The zeropage is supported in some VMAs,
+ * see vm_mixed_zeropage_allowed().
+ *
+ * The page has to be a nice clean _individual_ kernel allocation.
+ * If you allocate a compound page, you need to have marked it as
+ * such (__GFP_COMP), or manually just split the page up yourself
+ * (see split_page()).
+ *
+ * NOTE! Traditionally this was done with "remap_pfn_range()" which
+ * took an arbitrary page protection parameter. This doesn't allow
+ * that. Your vma protection will have to be set up correctly, which
+ * means that if you want a shared writable mapping, you'd better
+ * ask for a shared writable mapping!
+ *
+ * The page does not need to be reserved.
+ *
+ * Usually this function is called from f_op->mmap() handler
+ * under mm->mmap_lock write-lock, so it can change vma->vm_flags.
+ * Caller must set VM_MIXEDMAP on vma if it wants to call this
+ * function from other places, for example from page-fault handler.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
+			struct page *page)
+{
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return -EFAULT;
+	if (!(vma->vm_flags & VM_MIXEDMAP)) {
+		BUG_ON(mmap_read_trylock(vma->vm_mm));
+		BUG_ON(vma->vm_flags & VM_PFNMAP);
+		vm_flags_set(vma, VM_MIXEDMAP);
+	}
+	return insert_page(vma, addr, page, vma->vm_page_prot, false);
+}
+EXPORT_SYMBOL(vm_insert_page);
+
+/*
+ * __vm_map_pages - maps range of kernel pages into user vma
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ * @offset: user's requested vm_pgoff
+ *
+ * This allows drivers to map range of kernel pages into a user vma.
+ * The zeropage is supported in some VMAs, see
+ * vm_mixed_zeropage_allowed().
+ *
+ * Return: 0 on success and error code otherwise.
+ */
+static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
+				unsigned long num, unsigned long offset)
+{
+	unsigned long count = vma_pages(vma);
+	unsigned long uaddr = vma->vm_start;
+
+	/* Fail if the user requested offset is beyond the end of the object */
+	if (offset >= num)
+		return -ENXIO;
+
+	/* Fail if the user requested size exceeds available object size */
+	if (count > num - offset)
+		return -ENXIO;
+
+	return vm_insert_pages(vma, uaddr, pages + offset, &count);
+}
+
+/**
+ * vm_map_pages - maps range of kernel pages starts with non zero offset
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ *
+ * Maps an object consisting of @num pages, catering for the user's
+ * requested vm_pgoff
+ *
+ * If we fail to insert any page into the vma, the function will return
+ * immediately leaving any previously inserted pages present.  Callers
+ * from the mmap handler may immediately return the error as their caller
+ * will destroy the vma, removing any successfully inserted pages. Other
+ * callers should make their own arrangements for calling unmap_region().
+ *
+ * Context: Process context. Called by mmap handlers.
+ * Return: 0 on success and error code otherwise.
+ */
+int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
+				unsigned long num)
+{
+	return __vm_map_pages(vma, pages, num, vma_start_pgoff(vma));
+}
+EXPORT_SYMBOL(vm_map_pages);
+
+/**
+ * vm_map_pages_zero - map range of kernel pages starts with zero offset
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ *
+ * Similar to vm_map_pages(), except that it explicitly sets the offset
+ * to 0. This function is intended for the drivers that did not consider
+ * vm_pgoff.
+ *
+ * Context: Process context. Called by mmap handlers.
+ * Return: 0 on success and error code otherwise.
+ */
+int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
+				unsigned long num)
+{
+	return __vm_map_pages(vma, pages, num, 0);
+}
+EXPORT_SYMBOL(vm_map_pages_zero);
+
+static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, pgprot_t prot, bool mkwrite)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	pte_t *pte, entry;
+	spinlock_t *ptl;
+
+	pte = get_locked_pte(mm, addr, &ptl);
+	if (!pte)
+		return VM_FAULT_OOM;
+	entry = ptep_get(pte);
+	if (!pte_none(entry)) {
+		if (mkwrite) {
+			/*
+			 * For read faults on private mappings the PFN passed
+			 * in may not match the PFN we have mapped if the
+			 * mapped PFN is a writeable COW page.  In the mkwrite
+			 * case we are creating a writable PTE for a shared
+			 * mapping and we expect the PFNs to match. If they
+			 * don't match, we are likely racing with block
+			 * allocation and mapping invalidation so just skip the
+			 * update.
+			 */
+			if (pte_pfn(entry) != pfn) {
+				WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry)));
+				goto out_unlock;
+			}
+			entry = pte_mkyoung(entry);
+			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+			if (ptep_set_access_flags(vma, addr, pte, entry, 1))
+				update_mmu_cache(vma, addr, pte);
+		}
+		goto out_unlock;
+	}
+
+	/* Ok, finally just insert the thing.. */
+	entry = pte_mkspecial(pfn_pte(pfn, prot));
+
+	if (mkwrite) {
+		entry = pte_mkyoung(entry);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	}
+
+	set_pte_at(mm, addr, pte, entry);
+	update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
+
+out_unlock:
+	pte_unmap_unlock(pte, ptl);
+	return VM_FAULT_NOPAGE;
+}
+
+/**
+ * vmf_insert_pfn_prot - insert single pfn into user vma with specified pgprot
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ * @pgprot: pgprot flags for the inserted page
+ *
+ * This is exactly like vmf_insert_pfn(), except that it allows drivers
+ * to override pgprot on a per-page basis.
+ *
+ * This only makes sense for IO mappings, and it makes no sense for
+ * COW mappings.  In general, using multiple vmas is preferable;
+ * vmf_insert_pfn_prot should only be used if using multiple VMAs is
+ * impractical.
+ *
+ * pgprot typically only differs from @vma->vm_page_prot when drivers set
+ * caching- and encryption bits different than those of @vma->vm_page_prot,
+ * because the caching- or encryption mode may not be known at mmap() time.
+ *
+ * This is ok as long as @vma->vm_page_prot is not used by the core vm
+ * to set caching and encryption bits for those vmas (except for COW pages).
+ * This is ensured by core vm only modifying these page table entries using
+ * functions that don't touch caching- or encryption bits, using pte_modify()
+ * if needed. (See for example mprotect()).
+ *
+ * Also when new page-table entries are created, this is only done using the
+ * fault() callback, and never using the value of vma->vm_page_prot,
+ * except for page-table entries that point to anonymous pages as the result
+ * of COW.
+ *
+ * Context: Process context.  May allocate using %GFP_KERNEL.
+ * Return: vm_fault_t value.
+ */
+vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, pgprot_t pgprot)
+{
+	/*
+	 * Technically, architectures with pte_special can avoid all these
+	 * restrictions (same for remap_pfn_range).  However we would like
+	 * consistency in testing and feature parity among all, so we should
+	 * try to keep these invariants in place for everybody.
+	 */
+	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+	BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
+						(VM_PFNMAP|VM_MIXEDMAP));
+	BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+	BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
+
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return VM_FAULT_SIGBUS;
+
+	if (!pfn_modify_allowed(pfn, pgprot))
+		return VM_FAULT_SIGBUS;
+
+	pfnmap_setup_cachemode_pfn(pfn, &pgprot);
+
+	return insert_pfn(vma, addr, pfn, pgprot, false);
+}
+EXPORT_SYMBOL(vmf_insert_pfn_prot);
+
+/**
+ * vmf_insert_pfn - insert single pfn into user vma
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ *
+ * Similar to vm_insert_page, this allows drivers to insert individual pages
+ * they've allocated into a user vma. Same comments apply.
+ *
+ * This function should only be called from a vm_ops->fault handler, and
+ * in that case the handler should return the result of this function.
+ *
+ * vma cannot be a COW mapping.
+ *
+ * As this is called only for pages that do not currently exist, we
+ * do not need to flush old virtual caches or the TLB.
+ *
+ * Context: Process context.  May allocate using %GFP_KERNEL.
+ * Return: vm_fault_t value.
+ */
+vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn)
+{
+	return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vmf_insert_pfn);
+
+static bool vm_mixed_ok(struct vm_area_struct *vma, unsigned long pfn,
+			bool mkwrite)
+{
+	if (unlikely(is_zero_pfn(pfn)) &&
+	    (mkwrite || !vm_mixed_zeropage_allowed(vma)))
+		return false;
+	/* these checks mirror the abort conditions in vm_normal_page */
+	if (vma->vm_flags & VM_MIXEDMAP)
+		return true;
+	if (is_zero_pfn(pfn))
+		return true;
+	return false;
+}
+
+static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pfn, bool mkwrite)
+{
+	pgprot_t pgprot = vma->vm_page_prot;
+	int err;
+
+	if (!vm_mixed_ok(vma, pfn, mkwrite))
+		return VM_FAULT_SIGBUS;
+
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return VM_FAULT_SIGBUS;
+
+	pfnmap_setup_cachemode_pfn(pfn, &pgprot);
+
+	if (!pfn_modify_allowed(pfn, pgprot))
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * If we don't have pte special, then we have to use the pfn_valid()
+	 * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
+	 * refcount the page if pfn_valid is true (hence insert_page rather
+	 * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
+	 * without pte special, it would there be refcounted as a normal page.
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pfn_valid(pfn)) {
+		struct page *page;
+
+		/*
+		 * At this point we are committed to insert_page()
+		 * regardless of whether the caller specified flags that
+		 * result in pfn_t_has_page() == false.
+		 */
+		page = pfn_to_page(pfn);
+		err = insert_page(vma, addr, page, pgprot, mkwrite);
+	} else {
+		return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
+	}
+
+	if (err == -ENOMEM)
+		return VM_FAULT_OOM;
+	if (err < 0 && err != -EBUSY)
+		return VM_FAULT_SIGBUS;
+
+	return VM_FAULT_NOPAGE;
+}
+
+vm_fault_t vmf_insert_page_mkwrite(struct vm_fault *vmf, struct page *page,
+			bool write)
+{
+	pgprot_t pgprot = vmf->vma->vm_page_prot;
+	unsigned long addr = vmf->address;
+	int err;
+
+	if (addr < vmf->vma->vm_start || addr >= vmf->vma->vm_end)
+		return VM_FAULT_SIGBUS;
+
+	err = insert_page(vmf->vma, addr, page, pgprot, write);
+	if (err == -ENOMEM)
+		return VM_FAULT_OOM;
+	if (err < 0 && err != -EBUSY)
+		return VM_FAULT_SIGBUS;
+
+	return VM_FAULT_NOPAGE;
+}
+EXPORT_SYMBOL_GPL(vmf_insert_page_mkwrite);
+
+vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn)
+{
+	return __vm_insert_mixed(vma, addr, pfn, false);
+}
+EXPORT_SYMBOL(vmf_insert_mixed);
+
+/*
+ *  If the insertion of PTE failed because someone else already added a
+ *  different entry in the mean time, we treat that as success as we assume
+ *  the same entry was actually inserted.
+ */
+vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pfn)
+{
+	return __vm_insert_mixed(vma, addr, pfn, true);
+}
+
+/*
+ * maps a range of physical memory into the requested pages. the old
+ * mappings are removed. any references to nonexistent pages results
+ * in null mappings (currently treated as "copy-on-access")
+ */
+static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pte_t *pte, *mapped_pte;
+	spinlock_t *ptl;
+	int err = 0;
+
+	mapped_pte = pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
+	if (!pte)
+		return -ENOMEM;
+	lazy_mmu_mode_enable();
+	do {
+		BUG_ON(!pte_none(ptep_get(pte)));
+		if (!pfn_modify_allowed(pfn, prot)) {
+			err = -EACCES;
+			break;
+		}
+		set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
+		pfn++;
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	lazy_mmu_mode_disable();
+	pte_unmap_unlock(mapped_pte, ptl);
+	return err;
+}
+
+static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return -ENOMEM;
+	VM_BUG_ON(pmd_trans_huge(*pmd));
+	do {
+		next = pmd_addr_end(addr, end);
+		err = remap_pte_range(mm, pmd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pud_t *pud;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pud = pud_alloc(mm, p4d, addr);
+	if (!pud)
+		return -ENOMEM;
+	do {
+		next = pud_addr_end(addr, end);
+		err = remap_pmd_range(mm, pud, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return -ENOMEM;
+	do {
+		next = p4d_addr_end(addr, end);
+		err = remap_pud_range(mm, p4d, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (p4d++, addr = next, addr != end);
+	return 0;
+}
+
+static int get_remap_pgoff(bool is_cow, unsigned long addr,
+		unsigned long end, unsigned long vm_start, unsigned long vm_end,
+		unsigned long pfn, pgoff_t *vm_pgoff_p)
+{
+	/*
+	 * There's a horrible special case to handle copy-on-write
+	 * behaviour that some programs depend on. We mark the "original"
+	 * un-COW'ed pages by matching them up with "vma->vm_pgoff".
+	 * See vm_normal_page() for details.
+	 */
+	if (is_cow) {
+		if (addr != vm_start || end != vm_end)
+			return -EINVAL;
+		*vm_pgoff_p = pfn;
+	}
+
+	return 0;
+}
+
+static int remap_pfn_range_internal(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	pgd_t *pgd;
+	unsigned long next;
+	unsigned long end = addr + PAGE_ALIGN(size);
+	struct mm_struct *mm = vma->vm_mm;
+	int err;
+
+	if (WARN_ON_ONCE(!PAGE_ALIGNED(addr)))
+		return -EINVAL;
+
+	VM_WARN_ON_ONCE(!vma_test_all_mask(vma, VMA_REMAP_FLAGS));
+
+	BUG_ON(addr >= end);
+	pfn -= addr >> PAGE_SHIFT;
+	pgd = pgd_offset(mm, addr);
+	flush_cache_range(vma, addr, end);
+	do {
+		next = pgd_addr_end(addr, end);
+		err = remap_p4d_range(mm, pgd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (pgd++, addr = next, addr != end);
+
+	return 0;
+}
+
+/*
+ * Variant of remap_pfn_range that does not call track_pfn_remap.  The caller
+ * must have pre-validated the caching bits of the pgprot_t.
+ */
+static int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	int error = remap_pfn_range_internal(vma, addr, pfn, size, prot);
+
+	if (!error)
+		return 0;
+
+	/*
+	 * A partial pfn range mapping is dangerous: it does not
+	 * maintain page reference counts, and callers may free
+	 * pages due to the error. So zap it early.
+	 */
+	zap_vma_range(vma, addr, size);
+	return error;
+}
+
+#ifdef __HAVE_PFNMAP_TRACKING
+static inline struct pfnmap_track_ctx *pfnmap_track_ctx_alloc(unsigned long pfn,
+		unsigned long size, pgprot_t *prot)
+{
+	struct pfnmap_track_ctx *ctx;
+
+	if (pfnmap_track(pfn, size, prot))
+		return ERR_PTR(-EINVAL);
+
+	ctx = kmalloc_obj(*ctx);
+	if (unlikely(!ctx)) {
+		pfnmap_untrack(pfn, size);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	ctx->pfn = pfn;
+	ctx->size = size;
+	kref_init(&ctx->kref);
+	return ctx;
+}
+
+void pfnmap_track_ctx_release(struct kref *ref)
+{
+	struct pfnmap_track_ctx *ctx = container_of(ref, struct pfnmap_track_ctx, kref);
+
+	pfnmap_untrack(ctx->pfn, ctx->size);
+	kfree(ctx);
+}
+
+static int remap_pfn_range_track(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	struct pfnmap_track_ctx *ctx = NULL;
+	int err;
+
+	size = PAGE_ALIGN(size);
+
+	/*
+	 * If we cover the full VMA, we'll perform actual tracking, and
+	 * remember to untrack when the last reference to our tracking
+	 * context from a VMA goes away. We'll keep tracking the whole pfn
+	 * range even during VMA splits and partial unmapping.
+	 *
+	 * If we only cover parts of the VMA, we'll only setup the cachemode
+	 * in the pgprot for the pfn range.
+	 */
+	if (addr == vma->vm_start && addr + size == vma->vm_end) {
+		if (vma->pfnmap_track_ctx)
+			return -EINVAL;
+		ctx = pfnmap_track_ctx_alloc(pfn, size, &prot);
+		if (IS_ERR(ctx))
+			return PTR_ERR(ctx);
+	} else if (pfnmap_setup_cachemode(pfn, size, &prot)) {
+		return -EINVAL;
+	}
+
+	err = remap_pfn_range_notrack(vma, addr, pfn, size, prot);
+	if (ctx) {
+		if (err)
+			kref_put(&ctx->kref, pfnmap_track_ctx_release);
+		else
+			vma->pfnmap_track_ctx = ctx;
+	}
+	return err;
+}
+
+static int do_remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	return remap_pfn_range_track(vma, addr, pfn, size, prot);
+}
+#else
+static int do_remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	return remap_pfn_range_notrack(vma, addr, pfn, size, prot);
+}
+#endif
+
+int remap_pfn_range_prepare(struct vm_area_desc *desc)
+{
+	const struct mmap_action *action = &desc->action;
+	const unsigned long start = action->remap.start;
+	const unsigned long end = start + action->remap.size;
+	const unsigned long pfn = action->remap.start_pfn;
+	const bool is_cow = vma_desc_is_cow_mapping(desc);
+	int err;
+
+	if (!range_in_vma_desc(desc, start, end))
+		return -EFAULT;
+
+	err = get_remap_pgoff(is_cow, start, end, desc->start, desc->end, pfn,
+			      &desc->pgoff);
+	if (err)
+		return err;
+
+	vma_desc_set_flags_mask(desc, VMA_REMAP_FLAGS);
+	return 0;
+}
+
+static int remap_pfn_range_prepare_vma(struct vm_area_struct *vma,
+				       unsigned long addr, unsigned long pfn,
+				       unsigned long size)
+{
+	const unsigned long end = addr + PAGE_ALIGN(size);
+	const bool is_cow = is_cow_mapping(vma->vm_flags);
+	int err;
+
+	err = get_remap_pgoff(is_cow, addr, end, vma->vm_start, vma->vm_end,
+			      pfn, &vma->vm_pgoff);
+	if (err)
+		return err;
+
+	vma_set_flags_mask(vma, VMA_REMAP_FLAGS);
+	return 0;
+}
+
+/**
+ * remap_pfn_range - remap kernel memory to userspace
+ * @vma: user vma to map to
+ * @addr: target page aligned user address to start at
+ * @pfn: page frame number of kernel physical memory address
+ * @size: size of mapping area
+ * @prot: page protection flags for this mapping
+ *
+ * Note: this is only safe if the mm semaphore is held when called.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		    unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	int err;
+
+	err = remap_pfn_range_prepare_vma(vma, addr, pfn, size);
+	if (err)
+		return err;
+
+	return do_remap_pfn_range(vma, addr, pfn, size, prot);
+}
+EXPORT_SYMBOL(remap_pfn_range);
+
+int remap_pfn_range_complete(struct vm_area_struct *vma,
+			     struct mmap_action *action)
+{
+	const unsigned long start = action->remap.start;
+	const unsigned long pfn = action->remap.start_pfn;
+	const unsigned long size = action->remap.size;
+	const pgprot_t prot = action->remap.pgprot;
+
+	return do_remap_pfn_range(vma, start, pfn, size, prot);
+}
+
+static int __simple_ioremap_prep(unsigned long vm_len, pgoff_t vm_pgoff,
+				 phys_addr_t start_phys, unsigned long size,
+				 unsigned long *pfnp)
+{
+	unsigned long pfn, pages;
+
+	/* Check that the physical memory area passed in looks valid */
+	if (start_phys + size < start_phys)
+		return -EINVAL;
+	/*
+	 * You *really* shouldn't map things that aren't page-aligned,
+	 * but we've historically allowed it because IO memory might
+	 * just have smaller alignment.
+	 */
+	size += start_phys & ~PAGE_MASK;
+	pfn = start_phys >> PAGE_SHIFT;
+	pages = (size + ~PAGE_MASK) >> PAGE_SHIFT;
+	if (pfn + pages < pfn)
+		return -EINVAL;
+
+	/* We start the mapping 'vm_pgoff' pages into the area */
+	if (vm_pgoff > pages)
+		return -EINVAL;
+	pfn += vm_pgoff;
+	pages -= vm_pgoff;
+
+	/* Can we fit all of the mapping? */
+	if ((vm_len >> PAGE_SHIFT) > pages)
+		return -EINVAL;
+
+	*pfnp = pfn;
+	return 0;
+}
+
+int simple_ioremap_prepare(struct vm_area_desc *desc)
+{
+	struct mmap_action *action = &desc->action;
+	const phys_addr_t start = action->simple_ioremap.start_phys_addr;
+	const unsigned long size = action->simple_ioremap.size;
+	unsigned long pfn;
+	int err;
+
+	err = __simple_ioremap_prep(vma_desc_size(desc), desc->pgoff,
+				    start, size, &pfn);
+	if (err)
+		return err;
+
+	/* The I/O remap logic does the heavy lifting. */
+	mmap_action_ioremap_full(desc, pfn);
+	return io_remap_pfn_range_prepare(desc);
+}
+
+/**
+ * vm_iomap_memory - remap memory to userspace
+ * @vma: user vma to map to
+ * @start: start of the physical memory to be mapped
+ * @len: size of area
+ *
+ * This is a simplified io_remap_pfn_range() for common driver use. The
+ * driver just needs to give us the physical memory range to be mapped,
+ * we'll figure out the rest from the vma information.
+ *
+ * NOTE! Some drivers might want to tweak vma->vm_page_prot first to get
+ * whatever write-combining details or similar.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
+{
+	const unsigned long vm_start = vma->vm_start;
+	const unsigned long vm_end = vma->vm_end;
+	const unsigned long vm_len = vm_end - vm_start;
+	unsigned long pfn;
+	int err;
+
+	err = __simple_ioremap_prep(vm_len, vma_start_pgoff(vma), start, len,
+				    &pfn);
+	if (err)
+		return err;
+
+	/* Ok, let it rip */
+	return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_iomap_memory);
+
+static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data, bool create,
+				     pgtbl_mod_mask *mask)
+{
+	pte_t *pte, *mapped_pte;
+	int err = 0;
+	spinlock_t *ptl;
+
+	if (create) {
+		mapped_pte = pte = (mm == &init_mm) ?
+			pte_alloc_kernel_track(pmd, addr, mask) :
+			pte_alloc_map_lock(mm, pmd, addr, &ptl);
+		if (!pte)
+			return -ENOMEM;
+	} else {
+		mapped_pte = pte = (mm == &init_mm) ?
+			pte_offset_kernel(pmd, addr) :
+			pte_offset_map_lock(mm, pmd, addr, &ptl);
+		if (!pte)
+			return -EINVAL;
+	}
+
+	lazy_mmu_mode_enable();
+
+	if (fn) {
+		do {
+			if (create || !pte_none(ptep_get(pte))) {
+				err = fn(pte, addr, data);
+				if (err)
+					break;
+			}
+		} while (pte++, addr += PAGE_SIZE, addr != end);
+	}
+	*mask |= PGTBL_PTE_MODIFIED;
+
+	lazy_mmu_mode_disable();
+
+	if (mm != &init_mm)
+		pte_unmap_unlock(mapped_pte, ptl);
+	return err;
+}
+
+static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data, bool create,
+				     pgtbl_mod_mask *mask)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int err = 0;
+
+	BUG_ON(pud_leaf(*pud));
+
+	if (create) {
+		pmd = pmd_alloc_track(mm, pud, addr, mask);
+		if (!pmd)
+			return -ENOMEM;
+	} else {
+		pmd = pmd_offset(pud, addr);
+	}
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none(*pmd) && !create)
+			continue;
+		if (WARN_ON_ONCE(pmd_leaf(*pmd)))
+			return -EINVAL;
+		if (!pmd_none(*pmd) && WARN_ON_ONCE(pmd_bad(*pmd))) {
+			if (!create)
+				continue;
+			pmd_clear_bad(pmd);
+		}
+		err = apply_to_pte_range(mm, pmd, addr, next,
+					 fn, data, create, mask);
+		if (err)
+			break;
+	} while (pmd++, addr = next, addr != end);
+
+	return err;
+}
+
+static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data, bool create,
+				     pgtbl_mod_mask *mask)
+{
+	pud_t *pud;
+	unsigned long next;
+	int err = 0;
+
+	if (create) {
+		pud = pud_alloc_track(mm, p4d, addr, mask);
+		if (!pud)
+			return -ENOMEM;
+	} else {
+		pud = pud_offset(p4d, addr);
+	}
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none(*pud) && !create)
+			continue;
+		if (WARN_ON_ONCE(pud_leaf(*pud)))
+			return -EINVAL;
+		if (!pud_none(*pud) && WARN_ON_ONCE(pud_bad(*pud))) {
+			if (!create)
+				continue;
+			pud_clear_bad(pud);
+		}
+		err = apply_to_pmd_range(mm, pud, addr, next,
+					 fn, data, create, mask);
+		if (err)
+			break;
+	} while (pud++, addr = next, addr != end);
+
+	return err;
+}
+
+static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data, bool create,
+				     pgtbl_mod_mask *mask)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int err = 0;
+
+	if (create) {
+		p4d = p4d_alloc_track(mm, pgd, addr, mask);
+		if (!p4d)
+			return -ENOMEM;
+	} else {
+		p4d = p4d_offset(pgd, addr);
+	}
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none(*p4d) && !create)
+			continue;
+		if (WARN_ON_ONCE(p4d_leaf(*p4d)))
+			return -EINVAL;
+		if (!p4d_none(*p4d) && WARN_ON_ONCE(p4d_bad(*p4d))) {
+			if (!create)
+				continue;
+			p4d_clear_bad(p4d);
+		}
+		err = apply_to_pud_range(mm, p4d, addr, next,
+					 fn, data, create, mask);
+		if (err)
+			break;
+	} while (p4d++, addr = next, addr != end);
+
+	return err;
+}
+
+static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+				 unsigned long size, pte_fn_t fn,
+				 void *data, bool create)
+{
+	pgd_t *pgd;
+	unsigned long start = addr, next;
+	unsigned long end = addr + size;
+	pgtbl_mod_mask mask = 0;
+	int err = 0;
+
+	if (WARN_ON(addr >= end))
+		return -EINVAL;
+
+	pgd = pgd_offset(mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none(*pgd) && !create)
+			continue;
+		if (WARN_ON_ONCE(pgd_leaf(*pgd))) {
+			err = -EINVAL;
+			break;
+		}
+		if (!pgd_none(*pgd) && WARN_ON_ONCE(pgd_bad(*pgd))) {
+			if (!create)
+				continue;
+			pgd_clear_bad(pgd);
+		}
+		err = apply_to_p4d_range(mm, pgd, addr, next,
+					 fn, data, create, &mask);
+		if (err)
+			break;
+	} while (pgd++, addr = next, addr != end);
+
+	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
+		arch_sync_kernel_mappings(start, start + size);
+
+	return err;
+}
+
+/*
+ * Scan a region of virtual memory, filling in page tables as necessary
+ * and calling a provided function on each leaf page table.
+ */
+int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+			unsigned long size, pte_fn_t fn, void *data)
+{
+	return __apply_to_page_range(mm, addr, size, fn, data, true);
+}
+EXPORT_SYMBOL_GPL(apply_to_page_range);
+
+/*
+ * Scan a region of virtual memory, calling a provided function on
+ * each leaf page table where it exists.
+ *
+ * Unlike apply_to_page_range, this does _not_ fill in page tables
+ * where they are absent.
+ */
+int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
+				 unsigned long size, pte_fn_t fn, void *data)
+{
+	return __apply_to_page_range(mm, addr, size, fn, data, false);
+}
+
+/*
+ * handle_pte_fault chooses page fault handler according to an entry which was
+ * read non-atomically.  Before making any commitment, on those architectures
+ * or configurations (e.g. i386 with PAE) which might give a mix of unmatched
+ * parts, do_swap_page must check under lock before unmapping the pte and
+ * proceeding (but do_wp_page is only called after already making such a check;
+ * and do_anonymous_page can safely check later on).
+ */
+static inline int pte_unmap_same(struct vm_fault *vmf)
+{
+	int same = 1;
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION)
+	if (sizeof(pte_t) > sizeof(unsigned long)) {
+		spin_lock(vmf->ptl);
+		same = pte_same(ptep_get(vmf->pte), vmf->orig_pte);
+		spin_unlock(vmf->ptl);
+	}
+#endif
+	pte_unmap(vmf->pte);
+	vmf->pte = NULL;
+	return same;
+}
+
+/*
+ * Return:
+ *	0:		copied succeeded
+ *	-EHWPOISON:	copy failed due to hwpoison in source page
+ *	-EAGAIN:	copied failed (some other reason)
+ */
+static inline int __wp_page_copy_user(struct page *dst, struct page *src,
+				      struct vm_fault *vmf)
+{
+	int ret;
+	void *kaddr;
+	void __user *uaddr;
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr = vmf->address;
+
+	if (likely(src)) {
+		if (copy_mc_user_highpage(dst, src, addr, vma))
+			return -EHWPOISON;
+		return 0;
+	}
+
+	/*
+	 * If the source page was a PFN mapping, we don't have
+	 * a "struct page" for it. We do a best-effort copy by
+	 * just copying from the original user address. If that
+	 * fails, we just zero-fill it. Live with it.
+	 */
+	kaddr = kmap_local_page(dst);
+	pagefault_disable();
+	uaddr = (void __user *)(addr & PAGE_MASK);
+
+	/*
+	 * On architectures with software "accessed" bits, we would
+	 * take a double page fault, so mark it accessed here.
+	 */
+	vmf->pte = NULL;
+	if (!arch_has_hw_pte_young() && !pte_young(vmf->orig_pte)) {
+		pte_t entry;
+
+		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+		if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
+			/*
+			 * Other thread has already handled the fault
+			 * and update local tlb only
+			 */
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
+			ret = -EAGAIN;
+			goto pte_unlock;
+		}
+
+		entry = pte_mkyoung(vmf->orig_pte);
+		if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
+			update_mmu_cache_range(vmf, vma, addr, vmf->pte, 1);
+	}
+
+	/*
+	 * This really shouldn't fail, because the page is there
+	 * in the page tables. But it might just be unreadable,
+	 * in which case we just give up and fill the result with
+	 * zeroes.
+	 */
+	if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+		if (vmf->pte)
+			goto warn;
+
+		/* Re-validate under PTL if the page is still mapped */
+		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+		if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
+			/* The PTE changed under us, update local tlb */
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
+			ret = -EAGAIN;
+			goto pte_unlock;
+		}
+
+		/*
+		 * The same page can be mapped back since last copy attempt.
+		 * Try to copy again under PTL.
+		 */
+		if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+			/*
+			 * Give a warn in case there can be some obscure
+			 * use-case
+			 */
+warn:
+			WARN_ON_ONCE(1);
+			clear_page(kaddr);
+		}
+	}
+
+	ret = 0;
+
+pte_unlock:
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	pagefault_enable();
+	kunmap_local(kaddr);
+	flush_dcache_page(dst);
+
+	return ret;
+}
+
+static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
+{
+	struct file *vm_file = vma->vm_file;
+
+	if (vm_file)
+		return mapping_gfp_mask(vm_file->f_mapping) | __GFP_FS | __GFP_IO;
+
+	/*
+	 * Special mappings (e.g. VDSO) do not have any file so fake
+	 * a default GFP_KERNEL for them.
+	 */
+	return GFP_KERNEL;
+}
+
+/*
+ * Notify the address space that the page is about to become writable so that
+ * it can prohibit this or wait for the page to get into an appropriate state.
+ *
+ * We do this without the lock held, so that it can sleep if it needs to.
+ */
+static vm_fault_t do_page_mkwrite(struct vm_fault *vmf, struct folio *folio)
+{
+	vm_fault_t ret;
+	unsigned int old_flags = vmf->flags;
+
+	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
+
+	if (vmf->vma->vm_file &&
+	    IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
+		return VM_FAULT_SIGBUS;
+
+	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
+	/* Restore original flags so that caller is not surprised */
+	vmf->flags = old_flags;
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
+		return ret;
+	if (unlikely(!(ret & VM_FAULT_LOCKED))) {
+		folio_lock(folio);
+		if (!folio->mapping) {
+			folio_unlock(folio);
+			return 0; /* retry */
+		}
+		ret |= VM_FAULT_LOCKED;
+	} else
+		VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	return ret;
+}
+
+/*
+ * Handle dirtying of a page in shared file mapping on a write fault.
+ *
+ * The function expects the page to be locked and unlocks it.
+ */
+static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct address_space *mapping;
+	struct folio *folio = page_folio(vmf->page);
+	bool dirtied;
+	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
+
+	dirtied = folio_mark_dirty(folio);
+	VM_BUG_ON_FOLIO(folio_test_anon(folio), folio);
+	/*
+	 * Take a local copy of the address_space - folio.mapping may be zeroed
+	 * by truncate after folio_unlock().   The address_space itself remains
+	 * pinned by vma->vm_file's reference.  We rely on folio_unlock()'s
+	 * release semantics to prevent the compiler from undoing this copying.
+	 */
+	mapping = folio_raw_mapping(folio);
+	folio_unlock(folio);
+
+	if (!page_mkwrite)
+		file_update_time(vma->vm_file);
+
+	/*
+	 * Throttle page dirtying rate down to writeback speed.
+	 *
+	 * mapping may be NULL here because some device drivers do not
+	 * set page.mapping but still dirty their pages
+	 *
+	 * Drop the mmap_lock before waiting on IO, if we can. The file
+	 * is pinning the mapping, as per above.
+	 */
+	if ((dirtied || page_mkwrite) && mapping) {
+		struct file *fpin;
+
+		fpin = maybe_unlock_mmap_for_io(vmf, NULL);
+		balance_dirty_pages_ratelimited(mapping);
+		if (fpin) {
+			fput(fpin);
+			return VM_FAULT_COMPLETED;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Handle write page faults for pages that can be reused in the current vma
+ *
+ * This can happen either due to the mapping being with the VM_SHARED flag,
+ * or due to us being the last reference standing to the page. In either
+ * case, all we need to do here is to mark the page as writable and update
+ * any related book-keeping.
+ */
+static inline void wp_page_reuse(struct vm_fault *vmf, struct folio *folio)
+	__releases(vmf->ptl)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	pte_t entry;
+
+	VM_BUG_ON(!(vmf->flags & FAULT_FLAG_WRITE));
+	VM_WARN_ON(is_zero_pfn(pte_pfn(vmf->orig_pte)));
+
+	if (folio) {
+		VM_BUG_ON(folio_test_anon(folio) &&
+			  !PageAnonExclusive(vmf->page));
+		/*
+		 * Clear the folio's cpupid information as the existing
+		 * information potentially belongs to a now completely
+		 * unrelated process.
+		 */
+		folio_xchg_last_cpupid(folio, (1 << LAST_CPUPID_SHIFT) - 1);
+	}
+
+	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
+	entry = pte_mkyoung(vmf->orig_pte);
+	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
+		update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	count_vm_event(PGREUSE);
+}
+
+/*
+ * We could add a bitflag somewhere, but for now, we know that all
+ * vm_ops that have a ->map_pages have been audited and don't need
+ * the mmap_lock to be held.
+ */
+static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	if (vma->vm_ops->map_pages || !(vmf->flags & FAULT_FLAG_VMA_LOCK))
+		return 0;
+	vma_end_read(vma);
+	return VM_FAULT_RETRY;
+}
+
+/**
+ * __vmf_anon_prepare - Prepare to handle an anonymous fault.
+ * @vmf: The vm_fault descriptor passed from the fault handler.
+ *
+ * When preparing to insert an anonymous page into a VMA from a
+ * fault handler, call this function rather than anon_vma_prepare().
+ * If this vma does not already have an associated anon_vma and we are
+ * only protected by the per-VMA lock, the caller must retry with the
+ * mmap_lock held.  __anon_vma_prepare() will look at adjacent VMAs to
+ * determine if this VMA can share its anon_vma, and that's not safe to
+ * do with only the per-VMA lock held for this VMA.
+ *
+ * Return: 0 if fault handling can proceed.  Any other value should be
+ * returned to the caller.
+ */
+vm_fault_t __vmf_anon_prepare(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret = 0;
+
+	if (likely(vma->anon_vma))
+		return 0;
+	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+		if (!mmap_read_trylock(vma->vm_mm))
+			return VM_FAULT_RETRY;
+	}
+	if (__anon_vma_prepare(vma))
+		ret = VM_FAULT_OOM;
+	if (vmf->flags & FAULT_FLAG_VMA_LOCK)
+		mmap_read_unlock(vma->vm_mm);
+	return ret;
+}
+
+/*
+ * Handle the case of a page which we actually need to copy to a new page,
+ * either due to COW or unsharing.
+ *
+ * Called with either the VMA lock or the mmap_lock held (see FAULT_FLAG_VMA_LOCK)
+ * and the old page referenced, but without the ptl held.
+ *
+ * High level logic flow:
+ *
+ * - Allocate a page, copy the content of the old page to the new one.
+ * - Handle book keeping and accounting - cgroups, mmu-notifiers, etc.
+ * - Take the PTL. If the pte changed, bail out and release the allocated page
+ * - If the pte is still the way we remember it, update the page table and all
+ *   relevant references. This includes dropping the reference the page-table
+ *   held to the old page, as well as updating the rmap.
+ * - In any case, unlock the PTL and drop the reference we took to the old page.
+ */
+static vm_fault_t wp_page_copy(struct vm_fault *vmf)
+{
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	struct folio *old_folio = NULL;
+	struct folio *new_folio = NULL;
+	pte_t entry;
+	int page_copied = 0;
+	struct mmu_notifier_range range;
+	vm_fault_t ret;
+	bool pfn_is_zero;
+
+	delayacct_wpcopy_start();
+
+	if (vmf->page)
+		old_folio = page_folio(vmf->page);
+	ret = vmf_anon_prepare(vmf);
+	if (unlikely(ret))
+		goto out;
+
+	pfn_is_zero = is_zero_pfn(pte_pfn(vmf->orig_pte));
+	new_folio = folio_prealloc(mm, vma, vmf->address, pfn_is_zero);
+	if (!new_folio)
+		goto oom;
+
+	if (!pfn_is_zero) {
+		int err;
+
+		err = __wp_page_copy_user(&new_folio->page, vmf->page, vmf);
+		if (err) {
+			/*
+			 * COW failed, if the fault was solved by other,
+			 * it's fine. If not, userspace would re-fault on
+			 * the same address and we will handle the fault
+			 * from the second attempt.
+			 * The -EHWPOISON case will not be retried.
+			 */
+			folio_put(new_folio);
+			if (old_folio)
+				folio_put(old_folio);
+
+			delayacct_wpcopy_end();
+			return err == -EHWPOISON ? VM_FAULT_HWPOISON : 0;
+		}
+		kmsan_copy_page_meta(&new_folio->page, vmf->page);
+	}
+
+	__folio_mark_uptodate(new_folio);
+
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
+				vmf->address & PAGE_MASK,
+				(vmf->address & PAGE_MASK) + PAGE_SIZE);
+	mmu_notifier_invalidate_range_start(&range);
+
+	/*
+	 * Re-check the pte - we dropped the lock
+	 */
+	vmf->pte = pte_offset_map_lock(mm, vmf->pmd, vmf->address, &vmf->ptl);
+	if (likely(vmf->pte && pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
+		if (old_folio) {
+			if (!folio_test_anon(old_folio)) {
+				dec_mm_counter(mm, mm_counter_file(old_folio));
+				inc_mm_counter(mm, MM_ANONPAGES);
+			}
+		} else {
+			ksm_might_unmap_zero_page(mm, vmf->orig_pte);
+			inc_mm_counter(mm, MM_ANONPAGES);
+		}
+		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
+		entry = folio_mk_pte(new_folio, vma->vm_page_prot);
+		entry = pte_sw_mkyoung(entry);
+		if (unlikely(unshare)) {
+			if (pte_soft_dirty(vmf->orig_pte))
+				entry = pte_mksoft_dirty(entry);
+			if (pte_uffd(vmf->orig_pte))
+				entry = pte_mkuffd(entry);
+		} else {
+			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		}
+
+		/*
+		 * Clear the pte entry and flush it first, before updating the
+		 * pte with the new entry, to keep TLBs on different CPUs in
+		 * sync. This code used to set the new PTE then flush TLBs, but
+		 * that left a window where the new PTE could be loaded into
+		 * some TLBs while the old PTE remains in others.
+		 */
+		ptep_clear_flush(vma, vmf->address, vmf->pte);
+		folio_add_new_anon_rmap(new_folio, vma, vmf->address, RMAP_EXCLUSIVE);
+		folio_add_lru_vma(new_folio, vma);
+		BUG_ON(unshare && pte_write(entry));
+		set_pte_at(mm, vmf->address, vmf->pte, entry);
+		update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
+		if (old_folio) {
+			/*
+			 * Only after switching the pte to the new page may
+			 * we remove the mapcount here. Otherwise another
+			 * process may come and find the rmap count decremented
+			 * before the pte is switched to the new page, and
+			 * "reuse" the old page writing into it while our pte
+			 * here still points into it and can be read by other
+			 * threads.
+			 *
+			 * The critical issue is to order this
+			 * folio_remove_rmap_pte() with the ptp_clear_flush
+			 * above. Those stores are ordered by (if nothing else,)
+			 * the barrier present in the atomic_add_negative
+			 * in folio_remove_rmap_pte();
+			 *
+			 * Then the TLB flush in ptep_clear_flush ensures that
+			 * no process can access the old page before the
+			 * decremented mapcount is visible. And the old page
+			 * cannot be reused until after the decremented
+			 * mapcount is visible. So transitively, TLBs to
+			 * old page will be flushed before it can be reused.
+			 */
+			folio_remove_rmap_pte(old_folio, vmf->page, vma);
+		}
+
+		/* Free the old page.. */
+		new_folio = old_folio;
+		page_copied = 1;
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	} else if (vmf->pte) {
+		update_mmu_tlb(vma, vmf->address, vmf->pte);
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	}
+
+	mmu_notifier_invalidate_range_end(&range);
+
+	if (new_folio)
+		folio_put(new_folio);
+	if (old_folio) {
+		if (page_copied)
+			free_swap_cache(old_folio);
+		folio_put(old_folio);
+	}
+
+	delayacct_wpcopy_end();
+	return 0;
+oom:
+	ret = VM_FAULT_OOM;
+out:
+	if (old_folio)
+		folio_put(old_folio);
+
+	delayacct_wpcopy_end();
+	return ret;
+}
+
+/**
+ * finish_mkwrite_fault - finish page fault for a shared mapping, making PTE
+ *			  writeable once the page is prepared
+ *
+ * @vmf: structure describing the fault
+ * @folio: the folio of vmf->page
+ *
+ * This function handles all that is needed to finish a write page fault in a
+ * shared mapping due to PTE being read-only once the mapped page is prepared.
+ * It handles locking of PTE and modifying it.
+ *
+ * The function expects the page to be locked or other protection against
+ * concurrent faults / writeback (such as DAX radix tree locks).
+ *
+ * Return: %0 on success, %VM_FAULT_NOPAGE when PTE got changed before
+ * we acquired PTE lock.
+ */
+static vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf, struct folio *folio)
+{
+	WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));
+	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address,
+				       &vmf->ptl);
+	if (!vmf->pte)
+		return VM_FAULT_NOPAGE;
+	/*
+	 * We might have raced with another page fault while we released the
+	 * pte_offset_map_lock.
+	 */
+	if (!pte_same(ptep_get(vmf->pte), vmf->orig_pte)) {
+		update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return VM_FAULT_NOPAGE;
+	}
+	wp_page_reuse(vmf, folio);
+	return 0;
+}
+
+/*
+ * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED
+ * mapping
+ */
+static vm_fault_t wp_pfn_shared(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
+		vm_fault_t ret;
+
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		ret = vmf_can_call_fault(vmf);
+		if (ret)
+			return ret;
+
+		vmf->flags |= FAULT_FLAG_MKWRITE;
+		ret = vma->vm_ops->pfn_mkwrite(vmf);
+		if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
+			return ret;
+		return finish_mkwrite_fault(vmf, NULL);
+	}
+	wp_page_reuse(vmf, NULL);
+	return 0;
+}
+
+static vm_fault_t wp_page_shared(struct vm_fault *vmf, struct folio *folio)
+	__releases(vmf->ptl)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret = 0;
+
+	folio_get(folio);
+
+	if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+		vm_fault_t tmp;
+
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		tmp = vmf_can_call_fault(vmf);
+		if (tmp) {
+			folio_put(folio);
+			return tmp;
+		}
+
+		tmp = do_page_mkwrite(vmf, folio);
+		if (unlikely(!tmp || (tmp &
+				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+			folio_put(folio);
+			return tmp;
+		}
+		tmp = finish_mkwrite_fault(vmf, folio);
+		if (unlikely(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+			folio_unlock(folio);
+			folio_put(folio);
+			return tmp;
+		}
+	} else {
+		wp_page_reuse(vmf, folio);
+		folio_lock(folio);
+	}
+	ret |= fault_dirty_shared_page(vmf);
+	folio_put(folio);
+
+	return ret;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static bool __wp_can_reuse_large_anon_folio(struct folio *folio,
+		struct vm_area_struct *vma)
+{
+	bool exclusive = false;
+
+	/* Let's just free up a large folio if only a single page is mapped. */
+	if (folio_large_mapcount(folio) <= 1)
+		return false;
+
+	/*
+	 * The assumption for anonymous folios is that each page can only get
+	 * mapped once into each MM. The only exception are KSM folios, which
+	 * are always small.
+	 *
+	 * Each taken mapcount must be paired with exactly one taken reference,
+	 * whereby the refcount must be incremented before the mapcount when
+	 * mapping a page, and the refcount must be decremented after the
+	 * mapcount when unmapping a page.
+	 *
+	 * If all folio references are from mappings, and all mappings are in
+	 * the page tables of this MM, then this folio is exclusive to this MM.
+	 */
+	if (test_bit(FOLIO_MM_IDS_SHARED_BITNUM, &folio->_mm_ids))
+		return false;
+
+	VM_WARN_ON_ONCE(folio_test_ksm(folio));
+
+	if (unlikely(folio_test_swapcache(folio))) {
+		/*
+		 * Note: freeing up the swapcache will fail if some PTEs are
+		 * still swap entries.
+		 */
+		if (!folio_trylock(folio))
+			return false;
+		folio_free_swap(folio);
+		folio_unlock(folio);
+	}
+
+	if (folio_large_mapcount(folio) != folio_ref_count(folio))
+		return false;
+
+	/* Stabilize the mapcount vs. refcount and recheck. */
+	folio_lock_large_mapcount(folio);
+	VM_WARN_ON_ONCE_FOLIO(folio_large_mapcount(folio) > folio_ref_count(folio), folio);
+
+	if (test_bit(FOLIO_MM_IDS_SHARED_BITNUM, &folio->_mm_ids))
+		goto unlock;
+	if (folio_large_mapcount(folio) != folio_ref_count(folio))
+		goto unlock;
+
+	VM_WARN_ON_ONCE_FOLIO(folio_large_mapcount(folio) > folio_nr_pages(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(folio_entire_mapcount(folio), folio);
+	VM_WARN_ON_ONCE(folio_mm_id(folio, 0) != vma->vm_mm->mm_id &&
+			folio_mm_id(folio, 1) != vma->vm_mm->mm_id);
+
+	/*
+	 * Do we need the folio lock? Likely not. If there would have been
+	 * references from page migration/swapout, we would have detected
+	 * an additional folio reference and never ended up here.
+	 */
+	exclusive = true;
+unlock:
+	folio_unlock_large_mapcount(folio);
+	return exclusive;
+}
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE */
+static bool __wp_can_reuse_large_anon_folio(struct folio *folio,
+		struct vm_area_struct *vma)
+{
+	BUILD_BUG();
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+static bool wp_can_reuse_anon_folio(struct folio *folio,
+				    struct vm_area_struct *vma)
+{
+	const bool maybe_in_lru_cache = !folio_test_lru(folio);
+	const bool in_swapcache = folio_test_swapcache(folio);
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && folio_test_large(folio))
+		return __wp_can_reuse_large_anon_folio(folio, vma);
+
+	/*
+	 * We have to verify under folio lock: these early checks are
+	 * just an optimization to avoid locking the folio and freeing
+	 * the swapcache if there is little hope that we can reuse.
+	 *
+	 * KSM doesn't necessarily raise the folio refcount.
+	 */
+	if (folio_test_ksm(folio) ||
+	    folio_ref_count(folio) > 1 + maybe_in_lru_cache + in_swapcache)
+		return false;
+	if (maybe_in_lru_cache)
+		/*
+		 * We cannot easily detect+handle references from
+		 * remote LRU caches or references to LRU folios.
+		 */
+		lru_add_drain();
+	if (folio_ref_count(folio) > 1 + in_swapcache)
+		return false;
+	if (!folio_trylock(folio))
+		return false;
+	if (folio_test_swapcache(folio))
+		folio_free_swap(folio);
+	if (folio_test_ksm(folio) || folio_ref_count(folio) != 1) {
+		folio_unlock(folio);
+		return false;
+	}
+	/*
+	 * Ok, we've got the only folio reference from our mapping
+	 * and the folio is locked, it's dark out, and we're wearing
+	 * sunglasses. Hit it.
+	 */
+	folio_move_anon_rmap(folio, vma);
+	folio_unlock(folio);
+	return true;
+}
+
+/*
+ * This routine handles present pages, when
+ * * users try to write to a shared page (FAULT_FLAG_WRITE)
+ * * GUP wants to take a R/O pin on a possibly shared anonymous page
+ *   (FAULT_FLAG_UNSHARE)
+ *
+ * It is done by copying the page to a new address and decrementing the
+ * shared-page counter for the old page.
+ *
+ * Note that this routine assumes that the protection checks have been
+ * done by the caller (the low-level page fault routine in most cases).
+ * Thus, with FAULT_FLAG_WRITE, we can safely just mark it writable once we've
+ * done any necessary COW.
+ *
+ * In case of FAULT_FLAG_WRITE, we also mark the page dirty at this point even
+ * though the page will change only once the write actually happens. This
+ * avoids a few races, and potentially makes it more efficient.
+ *
+ * We enter with either the VMA lock or the mmap_lock held (see
+ * FAULT_FLAG_VMA_LOCK) and pte both mapped and locked. We return with
+ * the same lock still held, but pte unmapped and unlocked.
+ */
+static vm_fault_t do_wp_page(struct vm_fault *vmf)
+	__releases(vmf->ptl)
+{
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio = NULL;
+	pte_t pte;
+
+	if (likely(!unshare)) {
+		if (userfaultfd_pte_wp(vma, ptep_get(vmf->pte))) {
+			if (!userfaultfd_wp_async(vma)) {
+				pte_unmap_unlock(vmf->pte, vmf->ptl);
+				return handle_userfault(vmf, VM_UFFD_WP);
+			}
+
+			/*
+			 * Nothing needed (cache flush, TLB invalidations,
+			 * etc.) because we're only removing the uffd-wp bit,
+			 * which is completely invisible to the user.
+			 */
+			pte = pte_clear_uffd(ptep_get(vmf->pte));
+
+			set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
+			/*
+			 * Update this to be prepared for following up CoW
+			 * handling
+			 */
+			vmf->orig_pte = pte;
+		}
+
+		/*
+		 * Userfaultfd write-protect can defer flushes. Ensure the TLB
+		 * is flushed in this case before copying.
+		 */
+		if (unlikely(userfaultfd_wp(vmf->vma) &&
+			     mm_tlb_flush_pending(vmf->vma->vm_mm)))
+			flush_tlb_page(vmf->vma, vmf->address);
+	}
+
+	vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte);
+
+	if (vmf->page)
+		folio = page_folio(vmf->page);
+
+	/*
+	 * Shared mapping: we are guaranteed to have VM_WRITE and
+	 * FAULT_FLAG_WRITE set at this point.
+	 */
+	if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
+		/*
+		 * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
+		 * VM_PFNMAP VMA. FS DAX also wants ops->pfn_mkwrite called.
+		 *
+		 * We should not cow pages in a shared writeable mapping.
+		 * Just mark the pages writable and/or call ops->pfn_mkwrite.
+		 */
+		if (!vmf->page || is_fsdax_page(vmf->page)) {
+			vmf->page = NULL;
+			return wp_pfn_shared(vmf);
+		}
+		return wp_page_shared(vmf, folio);
+	}
+
+	/*
+	 * Private mapping: create an exclusive anonymous page copy if reuse
+	 * is impossible. We might miss VM_WRITE for FOLL_FORCE handling.
+	 *
+	 * If we encounter a page that is marked exclusive, we must reuse
+	 * the page without further checks.
+	 */
+	if (folio && folio_test_anon(folio) &&
+	    (PageAnonExclusive(vmf->page) || wp_can_reuse_anon_folio(folio, vma))) {
+		if (!PageAnonExclusive(vmf->page))
+			SetPageAnonExclusive(vmf->page);
+		if (unlikely(unshare)) {
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return 0;
+		}
+		wp_page_reuse(vmf, folio);
+		return 0;
+	}
+	/*
+	 * Ok, we need to copy. Oh, well..
+	 */
+	if (folio)
+		folio_get(folio);
+
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+#ifdef CONFIG_KSM
+	if (folio && folio_test_ksm(folio))
+		count_vm_event(COW_KSM);
+#endif
+	return wp_page_copy(vmf);
+}
+
+static inline void unmap_mapping_range_tree(struct address_space *mapping,
+					    pgoff_t first_index,
+					    pgoff_t last_index,
+					    struct zap_details *details)
+{
+	struct vm_area_struct *vma;
+	struct mmu_gather tlb;
+
+	mapping_rmap_tree_foreach(vma, mapping, first_index, last_index) {
+		const pgoff_t start_idx = max(first_index, vma_start_pgoff(vma));
+		const pgoff_t end_idx = min(last_index, vma_last_pgoff(vma)) + 1;
+		const pgoff_t offset = start_idx - vma_start_pgoff(vma);
+		const unsigned long offset_bytes = offset << PAGE_SHIFT;
+		const unsigned long start = vma->vm_start + offset_bytes;
+		const unsigned long size = (end_idx - start_idx) << PAGE_SHIFT;
+
+		tlb_gather_mmu(&tlb, vma->vm_mm);
+		zap_vma_range_batched(&tlb, vma, start, size, details);
+		tlb_finish_mmu(&tlb);
+	}
+}
+
+/**
+ * unmap_mapping_folio() - Unmap single folio from processes.
+ * @folio: The locked folio to be unmapped.
+ *
+ * Unmap this folio from any userspace process which still has it mmaped.
+ * Typically, for efficiency, the range of nearby pages has already been
+ * unmapped by unmap_mapping_pages() or unmap_mapping_range().  But once
+ * truncation or invalidation holds the lock on a folio, it may find that
+ * the page has been remapped again: and then uses unmap_mapping_folio()
+ * to unmap it finally.
+ */
+void unmap_mapping_folio(struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+	struct zap_details details = { };
+	pgoff_t	first_index;
+	pgoff_t	last_index;
+
+	VM_BUG_ON(!folio_test_locked(folio));
+
+	first_index = folio->index;
+	last_index = folio_next_index(folio) - 1;
+
+	details.skip_cows = true;
+	details.single_folio = folio;
+	details.zap_flags = ZAP_FLAG_DROP_MARKER;
+
+	i_mmap_lock_read(mapping);
+	if (unlikely(mapping_mapped(mapping)))
+		unmap_mapping_range_tree(mapping, first_index,
+					 last_index, &details);
+	i_mmap_unlock_read(mapping);
+}
+
+/**
+ * unmap_mapping_pages() - Unmap pages from processes.
+ * @mapping: The address space containing pages to be unmapped.
+ * @start: Index of first page to be unmapped.
+ * @nr: Number of pages to be unmapped.  0 to unmap to end of file.
+ * @even_cows: Whether to unmap even private COWed pages.
+ *
+ * Unmap the pages in this address space from any userspace process which
+ * has them mmaped.  Generally, you want to remove COWed pages as well when
+ * a file is being truncated, but not when invalidating pages from the page
+ * cache.
+ */
+void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
+		pgoff_t nr, bool even_cows)
+{
+	struct zap_details details = { };
+	pgoff_t	first_index = start;
+	pgoff_t	last_index = start + nr - 1;
+
+	details.skip_cows = !even_cows;
+	if (last_index < first_index)
+		last_index = ULONG_MAX;
+
+	i_mmap_lock_read(mapping);
+	if (unlikely(mapping_mapped(mapping)))
+		unmap_mapping_range_tree(mapping, first_index,
+					 last_index, &details);
+	i_mmap_unlock_read(mapping);
+}
+EXPORT_SYMBOL_GPL(unmap_mapping_pages);
+
+/**
+ * unmap_mapping_range - unmap the portion of all mmaps in the specified
+ * address_space corresponding to the specified byte range in the underlying
+ * file.
+ *
+ * @mapping: the address space containing mmaps to be unmapped.
+ * @holebegin: byte in first page to unmap, relative to the start of
+ * the underlying file.  This will be rounded down to a PAGE_SIZE
+ * boundary.  Note that this is different from truncate_pagecache(), which
+ * must keep the partial page.  In contrast, we must get rid of
+ * partial pages.
+ * @holelen: size of prospective hole in bytes.  This will be rounded
+ * up to a PAGE_SIZE boundary.  A holelen of zero truncates to the
+ * end of the file.
+ * @even_cows: 1 when truncating a file, unmap even private COWed pages;
+ * but 0 when invalidating pagecache, don't throw away private data.
+ */
+void unmap_mapping_range(struct address_space *mapping,
+		loff_t const holebegin, loff_t const holelen, int even_cows)
+{
+	pgoff_t hba = (pgoff_t)(holebegin) >> PAGE_SHIFT;
+	pgoff_t hlen = ((pgoff_t)(holelen) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+	/* Check for overflow. */
+	if (sizeof(holelen) > sizeof(hlen)) {
+		long long holeend =
+			(holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		if (holeend & ~(long long)ULONG_MAX)
+			hlen = ULONG_MAX - hba + 1;
+	}
+
+	unmap_mapping_pages(mapping, hba, hlen, even_cows);
+}
+EXPORT_SYMBOL(unmap_mapping_range);
+
+/*
+ * Restore a potential device exclusive pte to a working pte entry
+ */
+static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
+{
+	struct folio *folio = page_folio(vmf->page);
+	struct vm_area_struct *vma = vmf->vma;
+	struct mmu_notifier_range range;
+	vm_fault_t ret;
+
+	/*
+	 * We need a reference to lock the folio because we don't hold
+	 * the PTL so a racing thread can remove the device-exclusive
+	 * entry and unmap it. If the folio is free the entry must
+	 * have been removed already. If it happens to have already
+	 * been re-allocated after being freed all we do is lock and
+	 * unlock it.
+	 */
+	if (!folio_try_get(folio))
+		return 0;
+
+	ret = folio_lock_or_retry(folio, vmf);
+	if (ret) {
+		folio_put(folio);
+		return ret;
+	}
+	mmu_notifier_range_init_owner(&range, MMU_NOTIFY_CLEAR, 0,
+				vma->vm_mm, vmf->address & PAGE_MASK,
+				(vmf->address & PAGE_MASK) + PAGE_SIZE, NULL);
+	mmu_notifier_invalidate_range_start(&range);
+
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
+				&vmf->ptl);
+	if (likely(vmf->pte && pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
+		restore_exclusive_pte(vma, folio, vmf->page, vmf->address,
+				      vmf->pte, vmf->orig_pte);
+
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	folio_unlock(folio);
+	folio_put(folio);
+
+	mmu_notifier_invalidate_range_end(&range);
+	return 0;
+}
+
+/*
+ * Check if we should call folio_free_swap to free the swap cache.
+ * folio_free_swap only frees the swap cache to release the slot if swap
+ * count is zero, so we don't need to check the swap count here.
+ */
+static inline bool should_try_to_free_swap(struct swap_info_struct *si,
+					   struct folio *folio,
+					   struct vm_area_struct *vma,
+					   bool exclusive,
+					   unsigned int fault_flags)
+{
+	if (!folio_test_swapcache(folio))
+		return false;
+	/*
+	 * Always try to free swap cache for SWP_SYNCHRONOUS_IO devices. Swap
+	 * cache can help save some IO or memory overhead, but these devices
+	 * are fast, and meanwhile, swap cache pinning the slot deferring the
+	 * release of metadata or fragmentation is a more critical issue.
+	 */
+	if (data_race(si->flags & SWP_SYNCHRONOUS_IO))
+		return true;
+	if (mem_cgroup_swap_full(folio) || (vma->vm_flags & VM_LOCKED) ||
+	    folio_test_mlocked(folio))
+		return true;
+
+	/*
+	 * Free the swapcache only if we are the exclusive user and
+	 * this is a write fault.
+	 */
+	return (fault_flags & FAULT_FLAG_WRITE) && exclusive;
+}
+
+static vm_fault_t pte_marker_clear(struct vm_fault *vmf)
+{
+	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
+				       vmf->address, &vmf->ptl);
+	if (!vmf->pte)
+		return 0;
+	/*
+	 * Be careful so that we will only recover a special uffd-wp pte into a
+	 * none pte.  Otherwise it means the pte could have changed, so retry.
+	 *
+	 * This should also cover the case where e.g. the pte changed
+	 * quickly from a PTE_MARKER_UFFD_WP into PTE_MARKER_POISONED.
+	 * So pte_is_marker() check is not enough to safely drop the pte.
+	 */
+	if (pte_same(vmf->orig_pte, ptep_get(vmf->pte)))
+		pte_clear(vmf->vma->vm_mm, vmf->address, vmf->pte);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return 0;
+}
+
+static vm_fault_t do_pte_missing(struct vm_fault *vmf)
+{
+	if (vma_is_anonymous(vmf->vma))
+		return do_anonymous_page(vmf);
+	else
+		return do_fault(vmf);
+}
+
+/*
+ * This is actually a page-missing access, but with uffd-wp special pte
+ * installed.  It means this pte was wr-protected before being unmapped.
+ */
+static vm_fault_t pte_marker_handle_uffd_wp(struct vm_fault *vmf)
+{
+	/*
+	 * Just in case there're leftover special ptes even after the region
+	 * got unregistered - we can simply clear them.
+	 */
+	if (unlikely(!userfaultfd_wp(vmf->vma)))
+		return pte_marker_clear(vmf);
+
+	return do_pte_missing(vmf);
+}
+
+static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
+{
+	const softleaf_t entry = softleaf_from_pte(vmf->orig_pte);
+	const pte_marker marker = softleaf_to_marker(entry);
+
+	/*
+	 * PTE markers should never be empty.  If anything weird happened,
+	 * the best thing to do is to kill the process along with its mm.
+	 */
+	if (WARN_ON_ONCE(!marker))
+		return VM_FAULT_SIGBUS;
+
+	/* Higher priority than uffd-wp when data corrupted */
+	if (marker & PTE_MARKER_POISONED)
+		return VM_FAULT_HWPOISON;
+
+	/* Hitting a guard page is always a fatal condition. */
+	if (marker & PTE_MARKER_GUARD)
+		return VM_FAULT_SIGSEGV;
+
+	if (softleaf_is_uffd_wp_marker(entry))
+		return pte_marker_handle_uffd_wp(vmf);
+
+	/* This is an unknown pte marker */
+	return VM_FAULT_SIGBUS;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/*
+ * Check if the PTEs within a range are contiguous swap entries.
+ */
+static bool can_swapin_thp(struct vm_fault *vmf, pte_t *ptep, int nr_pages)
+{
+	unsigned long addr;
+	int idx;
+	pte_t pte;
+
+	addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE);
+	idx = (vmf->address - addr) / PAGE_SIZE;
+	pte = ptep_get(ptep);
+
+	if (!pte_same(pte, pte_move_swp_offset(vmf->orig_pte, -idx)))
+		return false;
+	/*
+	 * swap_read_folio() can't handle the case a large folio is hybridly
+	 * from different backends. And they are likely corner cases. Similar
+	 * things might be added once zswap support large folios.
+	 */
+	if (swap_pte_batch(ptep, nr_pages, pte) != nr_pages)
+		return false;
+	return true;
+}
+
+static inline unsigned long thp_swap_suitable_orders(pgoff_t swp_offset,
+						     unsigned long addr,
+						     unsigned long orders)
+{
+	int order, nr;
+
+	order = highest_order(orders);
+
+	/*
+	 * To swap in a THP with nr pages, we require that its first swap_offset
+	 * is aligned with that number, as it was when the THP was swapped out.
+	 * This helps filter out most invalid entries.
+	 */
+	while (orders) {
+		nr = 1 << order;
+		if ((addr >> PAGE_SHIFT) % nr == swp_offset % nr)
+			break;
+		order = next_order(&orders, order);
+	}
+
+	return orders;
+}
+
+static unsigned long thp_swapin_suitable_orders(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long orders;
+	unsigned long addr;
+	softleaf_t entry;
+	spinlock_t *ptl;
+	pte_t *pte;
+	int order;
+
+	/*
+	 * If uffd is active for the vma we need per-page fault fidelity to
+	 * maintain the uffd semantics.
+	 */
+	if (unlikely(userfaultfd_armed(vma)))
+		return 0;
+
+	/*
+	 * A large swapped out folio could be partially or fully in zswap. We
+	 * lack handling for such cases, so fallback to swapping in order-0
+	 * folio.
+	 */
+	if (!zswap_never_enabled())
+		return 0;
+
+	entry = softleaf_from_pte(vmf->orig_pte);
+	/*
+	 * Get a list of all the (large) orders below PMD_ORDER that are enabled
+	 * and suitable for swapping THP.
+	 */
+	orders = thp_vma_allowable_orders(vma, vma->vm_flags, TVA_PAGEFAULT,
+					  BIT(PMD_ORDER) - 1);
+	orders = thp_vma_suitable_orders(vma, vmf->address, orders);
+	orders = thp_swap_suitable_orders(swp_offset(entry),
+					  vmf->address, orders);
+
+	if (!orders)
+		return 0;
+
+	pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
+				  vmf->address & PMD_MASK, &ptl);
+	if (unlikely(!pte))
+		return 0;
+
+	/*
+	 * For do_swap_page, find the highest order where the aligned range is
+	 * completely swap entries with contiguous swap offsets.
+	 */
+	order = highest_order(orders);
+	while (orders) {
+		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
+		if (can_swapin_thp(vmf, pte + pte_index(addr), 1 << order))
+			break;
+		order = next_order(&orders, order);
+	}
+
+	pte_unmap_unlock(pte, ptl);
+
+	return orders;
+}
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE */
+static unsigned long thp_swapin_suitable_orders(struct vm_fault *vmf)
+{
+	return 0;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+/* Sanity check that a folio is fully exclusive */
+static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,
+				 unsigned int nr_pages)
+{
+	/* Called under PT locked and folio locked, the swap count is stable */
+	do {
+		VM_WARN_ON_ONCE_FOLIO(__swap_count(entry) != 1, folio);
+		entry.val++;
+	} while (--nr_pages);
+}
+
+/*
+ * We enter with either the VMA lock or the mmap_lock held (see
+ * FAULT_FLAG_VMA_LOCK), and pte mapped but not yet locked.
+ * We return with pte unmapped and unlocked.
+ *
+ * When returning, the lock may have been released in the same cases
+ * as done by filemap_fault().
+ */
+vm_fault_t do_swap_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *swapcache = NULL, *folio;
+	struct page *page;
+	struct swap_info_struct *si = NULL;
+	rmap_t rmap_flags = RMAP_NONE;
+	bool exclusive = false;
+	bool rwp_restore = false;
+	softleaf_t entry;
+	pte_t pte;
+	vm_fault_t ret = 0;
+	int nr_pages;
+	unsigned long page_idx;
+	unsigned long address;
+	pte_t *ptep;
+
+	if (!pte_unmap_same(vmf))
+		goto out;
+
+	entry = softleaf_from_pte(vmf->orig_pte);
+	if (unlikely(!softleaf_is_swap(entry))) {
+		if (softleaf_is_migration(entry)) {
+			migration_entry_wait(vma->vm_mm, vmf->pmd,
+					     vmf->address);
+		} else if (softleaf_is_device_exclusive(entry)) {
+			vmf->page = softleaf_to_page(entry);
+			ret = remove_device_exclusive_entry(vmf);
+		} else if (softleaf_is_device_private(entry)) {
+			if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+				/*
+				 * migrate_to_ram is not yet ready to operate
+				 * under VMA lock.
+				 */
+				vma_end_read(vma);
+				ret = VM_FAULT_RETRY;
+				goto out;
+			}
+
+			vmf->page = softleaf_to_page(entry);
+			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+					vmf->address, &vmf->ptl);
+			if (unlikely(!vmf->pte ||
+				     !pte_same(ptep_get(vmf->pte),
+							vmf->orig_pte)))
+				goto unlock;
+
+			/*
+			 * Get a page reference while we know the page can't be
+			 * freed.
+			 */
+			if (trylock_page(vmf->page)) {
+				struct dev_pagemap *pgmap;
+
+				get_page(vmf->page);
+				pte_unmap_unlock(vmf->pte, vmf->ptl);
+				pgmap = page_pgmap(vmf->page);
+				ret = pgmap->ops->migrate_to_ram(vmf);
+				unlock_page(vmf->page);
+				put_page(vmf->page);
+			} else {
+				pte_unmap(vmf->pte);
+				softleaf_entry_wait_on_locked(entry, vmf->ptl);
+			}
+		} else if (softleaf_is_hwpoison(entry)) {
+			ret = VM_FAULT_HWPOISON;
+		} else if (softleaf_is_marker(entry)) {
+			ret = handle_pte_marker(vmf);
+		} else {
+			print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
+			ret = VM_FAULT_SIGBUS;
+		}
+		goto out;
+	}
+
+	/* Prevent swapoff from happening to us. */
+	si = get_swap_device(entry);
+	if (unlikely(!si))
+		goto out;
+
+	folio = swap_cache_get_folio(entry);
+	if (folio)
+		swap_update_readahead(folio, vma, vmf->address);
+	if (!folio) {
+		/* Swapin bypasses readahead for SWP_SYNCHRONOUS_IO devices */
+		if (data_race(si->flags & SWP_SYNCHRONOUS_IO))
+			folio = swapin_sync(entry, GFP_HIGHUSER_MOVABLE,
+					    thp_swapin_suitable_orders(vmf) | BIT(0),
+					    vmf, NULL, 0);
+		else
+			folio = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, vmf);
+
+		if (IS_ERR_OR_NULL(folio)) {
+			/*
+			 * Back out if somebody else faulted in this pte
+			 * while we released the pte lock.
+			 */
+			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+					vmf->address, &vmf->ptl);
+			if (likely(vmf->pte &&
+				   pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
+				ret = VM_FAULT_OOM;
+			folio = NULL;
+			goto unlock;
+		}
+
+		/* Had to read the page from swap area: Major fault */
+		ret = VM_FAULT_MAJOR;
+		count_vm_event(PGMAJFAULT);
+		count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
+	}
+
+	swapcache = folio;
+	ret |= folio_lock_or_retry(folio, vmf);
+	if (ret & VM_FAULT_RETRY)
+		goto out_release;
+
+	page = folio_file_page(folio, swp_offset(entry));
+	/*
+	 * Make sure folio_free_swap() or swapoff did not release the
+	 * swapcache from under us.  The page pin, and pte_same test
+	 * below, are not enough to exclude that.  Even if it is still
+	 * swapcache, we need to check that the page's swap has not
+	 * changed.
+	 */
+	if (unlikely(!folio_matches_swap_entry(folio, entry)))
+		goto out_page;
+
+	if (unlikely(PageHWPoison(page))) {
+		/*
+		 * hwpoisoned dirty swapcache pages are kept for killing
+		 * owner processes (which may be unknown at hwpoison time)
+		 */
+		ret = VM_FAULT_HWPOISON;
+		goto out_page;
+	}
+
+	/*
+	 * KSM sometimes has to copy on read faults, for example, if
+	 * folio->index of non-ksm folios would be nonlinear inside the
+	 * anon VMA -- the ksm flag is lost on actual swapout.
+	 */
+	folio = ksm_might_need_to_copy(folio, vma, vmf->address);
+	if (unlikely(!folio)) {
+		ret = VM_FAULT_OOM;
+		folio = swapcache;
+		goto out_page;
+	} else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
+		ret = VM_FAULT_HWPOISON;
+		folio = swapcache;
+		goto out_page;
+	} else if (folio != swapcache)
+		page = folio_page(folio, 0);
+
+	folio_throttle_swaprate(folio, GFP_KERNEL);
+
+	/*
+	 * Back out if somebody else already faulted in this pte.
+	 */
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
+			&vmf->ptl);
+	if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
+		goto out_nomap;
+
+	if (unlikely(!folio_test_uptodate(folio))) {
+		ret = VM_FAULT_SIGBUS;
+		goto out_nomap;
+	}
+
+	nr_pages = 1;
+	page_idx = 0;
+	address = vmf->address;
+	ptep = vmf->pte;
+	if (folio_test_large(folio) && folio_test_swapcache(folio)) {
+		int nr = folio_nr_pages(folio);
+		unsigned long idx = folio_page_idx(folio, page);
+		unsigned long folio_start = address - idx * PAGE_SIZE;
+		unsigned long folio_end = folio_start + nr * PAGE_SIZE;
+		pte_t *folio_ptep;
+		pte_t folio_pte;
+
+		if (unlikely(folio_start < max(address & PMD_MASK, vma->vm_start)))
+			goto check_folio;
+		if (unlikely(folio_end > pmd_addr_end(address, vma->vm_end)))
+			goto check_folio;
+
+		folio_ptep = vmf->pte - idx;
+		folio_pte = ptep_get(folio_ptep);
+		if (!pte_same(folio_pte, pte_move_swp_offset(vmf->orig_pte, -idx)) ||
+		    swap_pte_batch(folio_ptep, nr, folio_pte) != nr)
+			goto check_folio;
+
+		page_idx = idx;
+		address = folio_start;
+		ptep = folio_ptep;
+		nr_pages = nr;
+		entry = folio->swap;
+		page = &folio->page;
+	}
+
+check_folio:
+	/*
+	 * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte
+	 * must never point at an anonymous page in the swapcache that is
+	 * PG_anon_exclusive. Sanity check that this holds and especially, that
+	 * no filesystem set PG_mappedtodisk on a page in the swapcache. Sanity
+	 * check after taking the PT lock and making sure that nobody
+	 * concurrently faulted in this page and set PG_anon_exclusive.
+	 */
+	BUG_ON(!folio_test_anon(folio) && folio_test_mappedtodisk(folio));
+	BUG_ON(folio_test_anon(folio) && PageAnonExclusive(page));
+
+	/*
+	 * If a large folio already belongs to anon mapping, then we
+	 * can just go on and map it partially.
+	 * If not, with the large swapin check above failing, the page table
+	 * have changed, so sub pages might got charged to the wrong cgroup,
+	 * or even should be shmem. So we have to free it and fallback.
+	 * Nothing should have touched it, both anon and shmem checks if a
+	 * large folio is fully appliable before use.
+	 *
+	 * This will be removed once we unify folio allocation in the swap cache
+	 * layer, where allocation of a folio stabilizes the swap entries.
+	 */
+	if (!folio_test_anon(folio) && folio_test_large(folio) &&
+	    nr_pages != folio_nr_pages(folio)) {
+		if (!WARN_ON_ONCE(folio_test_dirty(folio)))
+			swap_cache_del_folio(folio);
+		goto out_nomap;
+	}
+
+	/*
+	 * Check under PT lock (to protect against concurrent fork() sharing
+	 * the swap entry concurrently) for certainly exclusive pages.
+	 */
+	if (!folio_test_ksm(folio)) {
+		/*
+		 * The can_swapin_thp check above ensures all PTE have
+		 * same exclusiveness. Checking just one PTE is fine.
+		 */
+		exclusive = pte_swp_exclusive(vmf->orig_pte);
+		if (exclusive)
+			check_swap_exclusive(folio, entry, nr_pages);
+		if (folio != swapcache) {
+			/*
+			 * We have a fresh page that is not exposed to the
+			 * swapcache -> certainly exclusive.
+			 */
+			exclusive = true;
+		} else if (exclusive && folio_test_writeback(folio) &&
+			  data_race(si->flags & SWP_STABLE_WRITES)) {
+			/*
+			 * This is tricky: not all swap backends support
+			 * concurrent page modifications while under writeback.
+			 *
+			 * So if we stumble over such a page in the swapcache
+			 * we must not set the page exclusive, otherwise we can
+			 * map it writable without further checks and modify it
+			 * while still under writeback.
+			 *
+			 * For these problematic swap backends, simply drop the
+			 * exclusive marker: this is perfectly fine as we start
+			 * writeback only if we fully unmapped the page and
+			 * there are no unexpected references on the page after
+			 * unmapping succeeded. After fully unmapped, no
+			 * further GUP references (FOLL_GET and FOLL_PIN) can
+			 * appear, so dropping the exclusive marker and mapping
+			 * it only R/O is fine.
+			 */
+			exclusive = false;
+		}
+	}
+
+	/*
+	 * Some architectures may have to restore extra metadata to the page
+	 * when reading from swap. This metadata may be indexed by swap entry
+	 * so this must be called before folio_put_swap().
+	 */
+	arch_swap_restore(folio_swap(entry, folio), folio);
+
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
+	add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
+	pte = mk_pte(page, vma->vm_page_prot);
+	if (pte_swp_soft_dirty(vmf->orig_pte))
+		pte = pte_mksoft_dirty(pte);
+	if (pte_swp_uffd(vmf->orig_pte))
+		pte = pte_mkuffd(pte);
+
+	/*
+	 * A page reclaimed while RWP-protected carries the uffd bit on
+	 * its swap entry. Re-apply PAGE_NONE on swap-in so the first access
+	 * still traps as an RWP fault. pte_modify() preserves _PAGE_UFFD.
+	 */
+	if (pte_swp_uffd(vmf->orig_pte) && userfaultfd_rwp(vma)) {
+		pte = pte_modify(pte, PAGE_NONE);
+		rwp_restore = true;
+	}
+
+	/*
+	 * Similar logic as in do_wp_page(); however, optimize for pages that
+	 * are certainly exclusive.
+	 *
+	 * Skip the write upgrade for an RWP-restored pte: it must stay
+	 * PROT_NONE so the access retries through the RWP fault path
+	 * (do_uffd_rwp()) rather than being made writable here.
+	 */
+	if (exclusive) {
+		if (!rwp_restore &&
+		    (vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
+		    !pte_needs_soft_dirty_wp(vma, pte)) {
+			pte = pte_mkwrite(pte, vma);
+			if (vmf->flags & FAULT_FLAG_WRITE)
+				pte = pte_mkdirty(pte);
+		}
+		rmap_flags |= RMAP_EXCLUSIVE;
+	}
+	folio_ref_add(folio, nr_pages - 1);
+	flush_icache_pages(vma, page, nr_pages);
+	vmf->orig_pte = pte_advance_pfn(pte, page_idx);
+
+	/* ksm created a completely new copy */
+	if (unlikely(folio != swapcache)) {
+		folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
+		folio_add_lru_vma(folio, vma);
+		folio_put_swap(swapcache, NULL);
+	} else if (!folio_test_anon(folio)) {
+		/*
+		 * We currently only expect !anon folios that are fully
+		 * mappable. See the comment after can_swapin_thp above.
+		 */
+		VM_WARN_ON_ONCE_FOLIO(folio_nr_pages(folio) != nr_pages, folio);
+		VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio);
+		folio_add_new_anon_rmap(folio, vma, address, rmap_flags);
+		folio_put_swap(folio, NULL);
+	} else {
+		VM_WARN_ON_ONCE(nr_pages != 1 && nr_pages != folio_nr_pages(folio));
+		folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
+					 rmap_flags);
+		folio_put_swap(folio, nr_pages == 1 ? page : NULL);
+	}
+
+	VM_BUG_ON(!folio_test_anon(folio) ||
+			(pte_write(pte) && !PageAnonExclusive(page)));
+	set_ptes(vma->vm_mm, address, ptep, pte, nr_pages);
+	arch_do_swap_page_nr(vma->vm_mm, vma, address,
+			pte, pte, nr_pages);
+
+	/*
+	 * Remove the swap entry and conditionally try to free up the swapcache.
+	 * Do it after mapping, so raced page faults will likely see the folio
+	 * in swap cache and wait on the folio lock.
+	 */
+	if (should_try_to_free_swap(si, folio, vma, exclusive, vmf->flags))
+		folio_free_swap(folio);
+
+	folio_unlock(folio);
+	if (unlikely(folio != swapcache)) {
+		/*
+		 * Hold the lock to avoid the swap entry to be reused
+		 * until we take the PT lock for the pte_same() check
+		 * (to avoid false positives from pte_same). For
+		 * further safety release the lock after the folio_put_swap
+		 * so that the swap count won't change under a
+		 * parallel locked swapcache.
+		 */
+		folio_unlock(swapcache);
+		folio_put(swapcache);
+	}
+
+	/*
+	 * For an RWP-restored pte, leave it PROT_NONE and let the write
+	 * retry through the RWP fault path; do not COW it here, which would
+	 * drop the marker for a non-exclusive page.
+	 */
+	if ((vmf->flags & FAULT_FLAG_WRITE) && !pte_write(pte) && !rwp_restore) {
+		ret |= do_wp_page(vmf);
+		if (ret & VM_FAULT_ERROR)
+			ret &= VM_FAULT_ERROR;
+		goto out;
+	}
+
+	/* No need to invalidate - it was non-present before */
+	update_mmu_cache_range(vmf, vma, address, ptep, nr_pages);
+unlock:
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+out:
+	if (si)
+		put_swap_device(si);
+	return ret;
+out_nomap:
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+out_page:
+	if (folio_test_swapcache(folio))
+		folio_free_swap(folio);
+	folio_unlock(folio);
+out_release:
+	folio_put(folio);
+	if (folio != swapcache) {
+		folio_unlock(swapcache);
+		folio_put(swapcache);
+	}
+	if (si)
+		put_swap_device(si);
+	return ret;
+}
+
+static bool pte_range_none(pte_t *pte, int nr_pages)
+{
+	int i;
+
+	for (i = 0; i < nr_pages; i++) {
+		if (!pte_none(ptep_get_lockless(pte + i)))
+			return false;
+	}
+
+	return true;
+}
+
+static struct folio *alloc_anon_folio(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	unsigned long orders;
+	struct folio *folio;
+	unsigned long addr;
+	pte_t *pte;
+	gfp_t gfp;
+	int order;
+
+	/*
+	 * If uffd is active for the vma we need per-page fault fidelity to
+	 * maintain the uffd semantics.
+	 */
+	if (unlikely(userfaultfd_armed(vma)))
+		goto fallback;
+
+	/*
+	 * Get a list of all the (large) orders below PMD_ORDER that are enabled
+	 * for this vma. Then filter out the orders that can't be allocated over
+	 * the faulting address and still be fully contained in the vma.
+	 */
+	orders = thp_vma_allowable_orders(vma, vma->vm_flags, TVA_PAGEFAULT,
+					  BIT(PMD_ORDER) - 1);
+	orders = thp_vma_suitable_orders(vma, vmf->address, orders);
+
+	if (!orders)
+		goto fallback;
+
+	pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK);
+	if (!pte)
+		return ERR_PTR(-EAGAIN);
+
+	/*
+	 * Find the highest order where the aligned range is completely
+	 * pte_none(). Note that all remaining orders will be completely
+	 * pte_none().
+	 */
+	order = highest_order(orders);
+	while (orders) {
+		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
+		if (pte_range_none(pte + pte_index(addr), 1 << order))
+			break;
+		order = next_order(&orders, order);
+	}
+
+	pte_unmap(pte);
+
+	if (!orders)
+		goto fallback;
+
+	/* Try allocating the highest of the remaining orders. */
+	gfp = vma_thp_gfp_mask(vma);
+	while (orders) {
+		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
+		folio = vma_alloc_folio(gfp, order, vma, addr);
+		if (!folio)
+			goto next;
+		if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
+			count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
+			folio_put(folio);
+			goto next;
+		}
+		if (order > 1 && folio_memcg_alloc_deferred(folio)) {
+			folio_put(folio);
+			goto fallback;
+		}
+		folio_throttle_swaprate(folio, gfp);
+		/*
+		 * When a folio is not zeroed during allocation
+		 * (__GFP_ZERO not used) or user folios require special
+		 * handling, folio_zero_user() is used to make sure
+		 * that the page corresponding to the faulting address
+		 * will be hot in the cache after zeroing.
+		 */
+		if (user_alloc_needs_zeroing())
+			folio_zero_user(folio, vmf->address);
+		return folio;
+next:
+		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
+		order = next_order(&orders, order);
+	}
+
+fallback:
+#endif
+	return folio_prealloc(vma->vm_mm, vma, vmf->address, true);
+}
+
+void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte,
+		struct vm_area_struct *vma, unsigned long addr,
+		bool uffd_wp)
+{
+	const unsigned int nr_pages = folio_nr_pages(folio);
+	pte_t entry = folio_mk_pte(folio, vma->vm_page_prot);
+
+	entry = pte_sw_mkyoung(entry);
+
+	if (vma->vm_flags & VM_WRITE)
+		entry = pte_mkwrite(pte_mkdirty(entry), vma);
+	if (uffd_wp)
+		entry = pte_mkuffd(entry);
+
+	folio_ref_add(folio, nr_pages - 1);
+	folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
+	folio_add_lru_vma(folio, vma);
+	set_ptes(vma->vm_mm, addr, pte, entry, nr_pages);
+	update_mmu_cache_range(NULL, vma, addr, pte, nr_pages);
+}
+
+static void map_anon_folio_pte_pf(struct folio *folio, pte_t *pte,
+		struct vm_area_struct *vma, unsigned long addr, bool uffd_wp)
+{
+	const unsigned int order = folio_order(folio);
+
+	map_anon_folio_pte_nopf(folio, pte, vma, addr, uffd_wp);
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1L << order);
+	count_mthp_stat(order, MTHP_STAT_ANON_FAULT_ALLOC);
+}
+
+/*
+ * We enter with either the VMA lock or the mmap_lock held (see
+ * FAULT_FLAG_VMA_LOCK), and pte unmapped and unlocked.
+ * We return with the lock still held, but pte unmapped and unlocked.
+ * If VM_FAULT_RETRY is returned, the lock may have been released.
+ */
+static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long addr = vmf->address;
+	struct folio *folio;
+	vm_fault_t ret = 0;
+	int nr_pages;
+	pte_t entry;
+
+	/* File mapping without ->vm_ops ? */
+	if (vma->vm_flags & VM_SHARED)
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Use pte_alloc() instead of pte_alloc_map(), so that OOM can
+	 * be distinguished from a transient failure of pte_offset_map().
+	 */
+	if (pte_alloc(vma->vm_mm, vmf->pmd))
+		return VM_FAULT_OOM;
+
+	/* Use the zero-page for reads */
+	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
+			!mm_forbids_zeropage(vma->vm_mm)) {
+		entry = pte_mkspecial(pfn_pte(zero_pfn(vmf->address),
+						vma->vm_page_prot));
+		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+				vmf->address, &vmf->ptl);
+		if (!vmf->pte)
+			goto unlock;
+		if (vmf_pte_changed(vmf)) {
+			update_mmu_tlb(vma, vmf->address, vmf->pte);
+			goto unlock;
+		}
+		ret = check_stable_address_space(vma->vm_mm);
+		if (ret)
+			goto unlock;
+		/* Deliver the page fault to userland, check inside PT lock */
+		if (userfaultfd_missing(vma)) {
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return handle_userfault(vmf, VM_UFFD_MISSING);
+		}
+		if (vmf_orig_pte_uffd_wp(vmf))
+			entry = pte_mkuffd(entry);
+		set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
+
+		/* No need to invalidate - it was non-present before */
+		update_mmu_cache(vma, addr, vmf->pte);
+		goto unlock;
+	}
+
+	/* Allocate our own private page. */
+	ret = vmf_anon_prepare(vmf);
+	if (ret)
+		return ret;
+	/* Returns NULL on OOM or ERR_PTR(-EAGAIN) if we must retry the fault */
+	folio = alloc_anon_folio(vmf);
+	if (IS_ERR(folio))
+		return 0;
+	if (!folio)
+		goto oom;
+
+	nr_pages = folio_nr_pages(folio);
+	addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE);
+
+	/*
+	 * The memory barrier inside __folio_mark_uptodate makes sure that
+	 * preceding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__folio_mark_uptodate(folio);
+
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
+	if (!vmf->pte)
+		goto release;
+	if (nr_pages == 1 && vmf_pte_changed(vmf)) {
+		update_mmu_tlb(vma, addr, vmf->pte);
+		goto release;
+	} else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
+		update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
+		goto release;
+	}
+
+	ret = check_stable_address_space(vma->vm_mm);
+	if (ret)
+		goto release;
+
+	/* Deliver the page fault to userland, check inside PT lock */
+	if (userfaultfd_missing(vma)) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		folio_put(folio);
+		return handle_userfault(vmf, VM_UFFD_MISSING);
+	}
+	map_anon_folio_pte_pf(folio, vmf->pte, vma, addr,
+			      vmf_orig_pte_uffd_wp(vmf));
+unlock:
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return ret;
+release:
+	folio_put(folio);
+	goto unlock;
+oom:
+	return VM_FAULT_OOM;
+}
+
+/*
+ * Either the VMA lock or the mmap_lock must have been held on entry
+ * (see FAULT_FLAG_VMA_LOCK) and may have been released depending on
+ * flags and vma->vm_ops->fault() return value.
+ * See filemap_fault() and __folio_lock_or_retry().
+ */
+static vm_fault_t __do_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio;
+	vm_fault_t ret;
+
+	/*
+	 * Preallocate pte before we take folio lock because this might lead to
+	 * deadlocks for memcg reclaim which waits for folios under writeback:
+	 *				folio_lock(A)
+	 *				folio_set_writeback(A)
+	 *				folio_unlock(A)
+	 * folio_lock(B)
+	 *				folio_lock(B)
+	 * pte_alloc_one
+	 *   shrink_folio_list
+	 *     folio_wait_writeback(A)
+	 *				folio_set_writeback(B)
+	 *				folio_unlock(B)
+	 *				# flush A, B to clear the writeback
+	 */
+	if (pmd_none(*vmf->pmd) && !vmf->prealloc_pte) {
+		vmf->prealloc_pte = pte_alloc_one(vma->vm_mm);
+		if (!vmf->prealloc_pte)
+			return VM_FAULT_OOM;
+	}
+
+	ret = vma->vm_ops->fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
+			    VM_FAULT_DONE_COW)))
+		return ret;
+
+	folio = page_folio(vmf->page);
+	if (unlikely(PageHWPoison(vmf->page))) {
+		vm_fault_t poisonret = VM_FAULT_HWPOISON;
+		if (ret & VM_FAULT_LOCKED) {
+			if (folio_mapped(folio))
+				unmap_mapping_folio(folio);
+			/* Retry if a clean folio was removed from the cache. */
+			if (mapping_evict_folio(folio->mapping, folio))
+				poisonret = VM_FAULT_NOPAGE;
+			folio_unlock(folio);
+		}
+		folio_put(folio);
+		vmf->page = NULL;
+		return poisonret;
+	}
+
+	if (unlikely(!(ret & VM_FAULT_LOCKED)))
+		folio_lock(folio);
+	else
+		VM_BUG_ON_PAGE(!folio_test_locked(folio), vmf->page);
+
+	return ret;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void deposit_prealloc_pte(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
+	/*
+	 * We are going to consume the prealloc table,
+	 * count that as nr_ptes.
+	 */
+	mm_inc_nr_ptes(vma->vm_mm);
+	vmf->prealloc_pte = NULL;
+}
+
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+	pmd_t entry;
+	vm_fault_t ret = VM_FAULT_FALLBACK;
+
+	/*
+	 * It is too late to allocate a small folio, we already have a large
+	 * folio in the pagecache: especially s390 KVM cannot tolerate any
+	 * PMD mappings, but PTE-mapped THP are fine. So let's simply refuse any
+	 * PMD mappings if THPs are disabled. As we already have a THP,
+	 * behave as if we are forcing a collapse.
+	 */
+	if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags,
+						     /* forced_collapse=*/ true))
+		return ret;
+
+	if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
+		return ret;
+
+	if (!is_pmd_order(folio_order(folio)))
+		return ret;
+	page = &folio->page;
+
+	/*
+	 * Just backoff if any subpage of a THP is corrupted otherwise
+	 * the corrupted page may mapped by PMD silently to escape the
+	 * check.  This kind of THP just can be PTE mapped.  Access to
+	 * the corrupted subpage should trigger SIGBUS as expected.
+	 */
+	if (unlikely(folio_test_has_hwpoisoned(folio)))
+		return ret;
+
+	/*
+	 * Archs like ppc64 need additional space to store information
+	 * related to pte entry. Use the preallocated table for that.
+	 */
+	if (arch_needs_pgtable_deposit() && !vmf->prealloc_pte) {
+		vmf->prealloc_pte = pte_alloc_one(vma->vm_mm);
+		if (!vmf->prealloc_pte)
+			return VM_FAULT_OOM;
+	}
+
+	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+	if (unlikely(!pmd_none(*vmf->pmd)))
+		goto out;
+
+	flush_icache_pages(vma, page, HPAGE_PMD_NR);
+
+	entry = folio_mk_pmd(folio, vma->vm_page_prot);
+	if (write)
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+
+	add_mm_counter(vma->vm_mm, mm_counter_file(folio), HPAGE_PMD_NR);
+	folio_add_file_rmap_pmd(folio, page, vma);
+
+	/*
+	 * deposit and withdraw with pmd lock held
+	 */
+	if (arch_needs_pgtable_deposit())
+		deposit_prealloc_pte(vmf);
+
+	set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
+
+	update_mmu_cache_pmd(vma, haddr, vmf->pmd);
+
+	/* fault is handled */
+	ret = 0;
+	count_vm_event(THP_FILE_MAPPED);
+out:
+	spin_unlock(vmf->ptl);
+	return ret;
+}
+#else
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
+{
+	return VM_FAULT_FALLBACK;
+}
+#endif
+
+/**
+ * set_pte_range - Set a range of PTEs to point to pages in a folio.
+ * @vmf: Fault description.
+ * @folio: The folio that contains @page.
+ * @page: The first page to create a PTE for.
+ * @nr: The number of PTEs to create.
+ * @addr: The first address to create a PTE for.
+ */
+void set_pte_range(struct vm_fault *vmf, struct folio *folio,
+		struct page *page, unsigned int nr, unsigned long addr)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	bool prefault = !in_range(vmf->address, addr, nr * PAGE_SIZE);
+	pte_t entry;
+
+	flush_icache_pages(vma, page, nr);
+	entry = mk_pte(page, vma->vm_page_prot);
+
+	if (prefault && arch_wants_old_prefaulted_pte())
+		entry = pte_mkold(entry);
+	else
+		entry = pte_sw_mkyoung(entry);
+
+	if (write)
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	else if (pte_write(entry) && folio_test_dirty(folio))
+		entry = pte_mkdirty(entry);
+	if (unlikely(vmf_orig_pte_uffd_wp(vmf)))
+		entry = pte_mkuffd(entry);
+	/* copy-on-write page */
+	if (write && !(vma->vm_flags & VM_SHARED)) {
+		VM_BUG_ON_FOLIO(nr != 1, folio);
+		folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
+		folio_add_lru_vma(folio, vma);
+	} else {
+		folio_add_file_rmap_ptes(folio, page, nr, vma);
+	}
+	set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
+
+	/* no need to invalidate: a not-present page won't be cached */
+	update_mmu_cache_range(vmf, vma, addr, vmf->pte, nr);
+}
+
+static bool vmf_pte_changed(struct vm_fault *vmf)
+{
+	if (vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)
+		return !pte_same(ptep_get(vmf->pte), vmf->orig_pte);
+
+	return !pte_none(ptep_get(vmf->pte));
+}
+
+/**
+ * finish_fault - finish page fault once we have prepared the page to fault
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a page fault once the
+ * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
+ * given page, adds reverse page mapping, handles memcg charges and LRU
+ * addition.
+ *
+ * The function expects the page to be locked and on success it consumes a
+ * reference of a page being mapped (for the PTE which maps it).
+ *
+ * Return: %0 on success, %VM_FAULT_ code in case of error.
+ */
+vm_fault_t finish_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page;
+	struct folio *folio;
+	vm_fault_t ret;
+	bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
+		      !(vma->vm_flags & VM_SHARED);
+	int type, nr_pages;
+	unsigned long addr;
+	bool needs_fallback = false;
+
+fallback:
+	addr = vmf->address;
+
+	/* Did we COW the page? */
+	if (is_cow)
+		page = vmf->cow_page;
+	else
+		page = vmf->page;
+
+	folio = page_folio(page);
+	/*
+	 * check even for read faults because we might have lost our CoWed
+	 * page
+	 */
+	if (!(vma->vm_flags & VM_SHARED)) {
+		ret = check_stable_address_space(vma->vm_mm);
+		if (ret)
+			return ret;
+	}
+
+	if (!needs_fallback && vma->vm_file) {
+		struct address_space *mapping = vma->vm_file->f_mapping;
+		pgoff_t file_end;
+
+		file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
+
+		/*
+		 * Do not allow to map with PTEs beyond i_size and with PMD
+		 * across i_size to preserve SIGBUS semantics.
+		 *
+		 * Make an exception for shmem/tmpfs that for long time
+		 * intentionally mapped with PMDs across i_size.
+		 */
+		needs_fallback = !shmem_mapping(mapping) &&
+			file_end < folio_next_index(folio);
+	}
+
+	if (pmd_none(*vmf->pmd)) {
+		if (!needs_fallback && folio_test_pmd_mappable(folio)) {
+			ret = do_set_pmd(vmf, folio, page);
+			if (ret != VM_FAULT_FALLBACK)
+				return ret;
+		}
+
+		if (vmf->prealloc_pte)
+			pmd_install(vma->vm_mm, vmf->pmd, &vmf->prealloc_pte);
+		else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd)))
+			return VM_FAULT_OOM;
+	}
+
+	nr_pages = folio_nr_pages(folio);
+
+	/* Using per-page fault to maintain the uffd semantics */
+	if (unlikely(userfaultfd_armed(vma)) || unlikely(needs_fallback)) {
+		nr_pages = 1;
+	} else if (nr_pages > 1) {
+		pgoff_t idx = folio_page_idx(folio, page);
+		/* The page offset of vmf->address within the VMA. */
+		pgoff_t vma_off = vmf->pgoff - vma_start_pgoff(vmf->vma);
+		/* The index of the entry in the pagetable for fault page. */
+		pgoff_t pte_off = pte_index(vmf->address);
+
+		/*
+		 * Fallback to per-page fault in case the folio size in page
+		 * cache beyond the VMA limits and PMD pagetable limits.
+		 */
+		if (unlikely(vma_off < idx ||
+			    vma_off + (nr_pages - idx) > vma_pages(vma) ||
+			    pte_off < idx ||
+			    pte_off + (nr_pages - idx)  > PTRS_PER_PTE)) {
+			nr_pages = 1;
+		} else {
+			/* Now we can set mappings for the whole large folio. */
+			addr = vmf->address - idx * PAGE_SIZE;
+			page = &folio->page;
+		}
+	}
+
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+				       addr, &vmf->ptl);
+	if (!vmf->pte)
+		return VM_FAULT_NOPAGE;
+
+	/* Re-check under ptl */
+	if (nr_pages == 1 && unlikely(vmf_pte_changed(vmf))) {
+		update_mmu_tlb(vma, addr, vmf->pte);
+		ret = VM_FAULT_NOPAGE;
+		goto unlock;
+	} else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
+		needs_fallback = true;
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		goto fallback;
+	}
+
+	folio_ref_add(folio, nr_pages - 1);
+	set_pte_range(vmf, folio, page, nr_pages, addr);
+	type = is_cow ? MM_ANONPAGES : mm_counter_file(folio);
+	add_mm_counter(vma->vm_mm, type, nr_pages);
+	ret = 0;
+
+unlock:
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return ret;
+}
+
+static unsigned long fault_around_pages __read_mostly =
+	65536 >> PAGE_SHIFT;
+
+#ifdef CONFIG_DEBUG_FS
+static int fault_around_bytes_get(void *data, u64 *val)
+{
+	*val = fault_around_pages << PAGE_SHIFT;
+	return 0;
+}
+
+/*
+ * fault_around_bytes must be rounded down to the nearest page order as it's
+ * what do_fault_around() expects to see.
+ */
+static int fault_around_bytes_set(void *data, u64 val)
+{
+	if (val / PAGE_SIZE > PTRS_PER_PTE)
+		return -EINVAL;
+
+	/*
+	 * The minimum value is 1 page, however this results in no fault-around
+	 * at all. See should_fault_around().
+	 */
+	val = max(val, PAGE_SIZE);
+	fault_around_pages = rounddown_pow_of_two(val) >> PAGE_SHIFT;
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(fault_around_bytes_fops,
+		fault_around_bytes_get, fault_around_bytes_set, "%llu\n");
+
+static int __init fault_around_debugfs(void)
+{
+	debugfs_create_file_unsafe("fault_around_bytes", 0644, NULL, NULL,
+				   &fault_around_bytes_fops);
+	return 0;
+}
+late_initcall(fault_around_debugfs);
+#endif
+
+/*
+ * do_fault_around() tries to map few pages around the fault address. The hope
+ * is that the pages will be needed soon and this will lower the number of
+ * faults to handle.
+ *
+ * It uses vm_ops->map_pages() to map the pages, which skips the page if it's
+ * not ready to be mapped: not up-to-date, locked, etc.
+ *
+ * This function doesn't cross VMA or page table boundaries, in order to call
+ * map_pages() and acquire a PTE lock only once.
+ *
+ * fault_around_pages defines how many pages we'll try to map.
+ * do_fault_around() expects it to be set to a power of two less than or equal
+ * to PTRS_PER_PTE.
+ *
+ * The virtual address of the area that we map is naturally aligned to
+ * fault_around_pages * PAGE_SIZE rounded down to the machine page size
+ * (and therefore to page order).  This way it's easier to guarantee
+ * that we don't cross page table boundaries.
+ */
+static vm_fault_t do_fault_around(struct vm_fault *vmf)
+{
+	pgoff_t nr_pages = READ_ONCE(fault_around_pages);
+	pgoff_t pte_off = pte_index(vmf->address);
+	/* The page offset of vmf->address within the VMA. */
+	pgoff_t vma_off = vmf->pgoff - vma_start_pgoff(vmf->vma);
+	pgoff_t from_pte, to_pte;
+	vm_fault_t ret;
+
+	/* The PTE offset of the start address, clamped to the VMA. */
+	from_pte = max(ALIGN_DOWN(pte_off, nr_pages),
+		       pte_off - min(pte_off, vma_off));
+
+	/* The PTE offset of the end address, clamped to the VMA and PTE. */
+	to_pte = min3(from_pte + nr_pages, (pgoff_t)PTRS_PER_PTE,
+		      pte_off + vma_pages(vmf->vma) - vma_off) - 1;
+
+	if (pmd_none(*vmf->pmd)) {
+		vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm);
+		if (!vmf->prealloc_pte)
+			return VM_FAULT_OOM;
+	}
+
+	rcu_read_lock();
+	ret = vmf->vma->vm_ops->map_pages(vmf,
+			vmf->pgoff + from_pte - pte_off,
+			vmf->pgoff + to_pte - pte_off);
+	rcu_read_unlock();
+
+	return ret;
+}
+
+/* Return true if we should do read fault-around, false otherwise */
+static inline bool should_fault_around(struct vm_fault *vmf)
+{
+	/* No ->map_pages?  No way to fault around... */
+	if (!vmf->vma->vm_ops->map_pages)
+		return false;
+
+	if (uffd_disable_fault_around(vmf->vma))
+		return false;
+
+	/* A single page implies no faulting 'around' at all. */
+	return fault_around_pages > 1;
+}
+
+static vm_fault_t do_read_fault(struct vm_fault *vmf)
+{
+	vm_fault_t ret = 0;
+	struct folio *folio;
+
+	/*
+	 * Let's call ->map_pages() first and use ->fault() as fallback
+	 * if page by the offset is not ready to be mapped (cold cache or
+	 * something).
+	 */
+	if (should_fault_around(vmf)) {
+		ret = do_fault_around(vmf);
+		if (ret)
+			return ret;
+	}
+
+	ret = vmf_can_call_fault(vmf);
+	if (ret)
+		return ret;
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		return ret;
+
+	ret |= finish_fault(vmf);
+	folio = page_folio(vmf->page);
+	folio_unlock(folio);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		folio_put(folio);
+	return ret;
+}
+
+static vm_fault_t do_cow_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio;
+	vm_fault_t ret;
+
+	ret = vmf_can_call_fault(vmf);
+	if (!ret)
+		ret = vmf_anon_prepare(vmf);
+	if (ret)
+		return ret;
+
+	folio = folio_prealloc(vma->vm_mm, vma, vmf->address, false);
+	if (!folio)
+		return VM_FAULT_OOM;
+
+	vmf->cow_page = &folio->page;
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		goto uncharge_out;
+	if (ret & VM_FAULT_DONE_COW)
+		return ret;
+
+	if (copy_mc_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma)) {
+		ret = VM_FAULT_HWPOISON;
+		goto unlock;
+	}
+	__folio_mark_uptodate(folio);
+
+	ret |= finish_fault(vmf);
+unlock:
+	unlock_page(vmf->page);
+	put_page(vmf->page);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		goto uncharge_out;
+	return ret;
+uncharge_out:
+	folio_put(folio);
+	return ret;
+}
+
+static vm_fault_t do_shared_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret, tmp;
+	struct folio *folio;
+
+	ret = vmf_can_call_fault(vmf);
+	if (ret)
+		return ret;
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		return ret;
+
+	folio = page_folio(vmf->page);
+
+	/*
+	 * Check if the backing address space wants to know that the page is
+	 * about to become writable
+	 */
+	if (vma->vm_ops->page_mkwrite) {
+		folio_unlock(folio);
+		tmp = do_page_mkwrite(vmf, folio);
+		if (unlikely(!tmp ||
+				(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+			folio_put(folio);
+			return tmp;
+		}
+	}
+
+	ret |= finish_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
+					VM_FAULT_RETRY))) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return ret;
+	}
+
+	ret |= fault_dirty_shared_page(vmf);
+	return ret;
+}
+
+/*
+ * We enter with either the VMA lock or the mmap_lock held (see
+ * FAULT_FLAG_VMA_LOCK).
+ * The lock may have been released depending on flags and our
+ * return value.  See filemap_fault() and __folio_lock_or_retry().
+ * If the lock is released, vma may become invalid (for example
+ * by other thread calling munmap()).
+ */
+static vm_fault_t do_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *vm_mm = vma->vm_mm;
+	vm_fault_t ret;
+
+	/*
+	 * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
+	 */
+	if (!vma->vm_ops->fault) {
+		vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
+					       vmf->address, &vmf->ptl);
+		if (unlikely(!vmf->pte))
+			ret = VM_FAULT_SIGBUS;
+		else {
+			/*
+			 * Make sure this is not a temporary clearing of pte
+			 * by holding ptl and checking again. A R/M/W update
+			 * of pte involves: take ptl, clearing the pte so that
+			 * we don't have concurrent modification by hardware
+			 * followed by an update.
+			 */
+			if (unlikely(pte_none(ptep_get(vmf->pte))))
+				ret = VM_FAULT_SIGBUS;
+			else
+				ret = VM_FAULT_NOPAGE;
+
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+		}
+	} else if (!(vmf->flags & FAULT_FLAG_WRITE))
+		ret = do_read_fault(vmf);
+	else if (!(vma->vm_flags & VM_SHARED))
+		ret = do_cow_fault(vmf);
+	else
+		ret = do_shared_fault(vmf);
+
+	/* preallocated pagetable is unused: free it */
+	if (vmf->prealloc_pte) {
+		pte_free(vm_mm, vmf->prealloc_pte);
+		vmf->prealloc_pte = NULL;
+	}
+	return ret;
+}
+
+int numa_migrate_check(struct folio *folio, struct vm_fault *vmf,
+		      unsigned long addr, int *flags,
+		      bool writable, int *last_cpupid)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	/*
+	 * Avoid grouping on RO pages in general. RO pages shouldn't hurt as
+	 * much anyway since they can be in shared cache state. This misses
+	 * the case where a mapping is writable but the process never writes
+	 * to it but pte_write gets cleared during protection updates and
+	 * pte_dirty has unpredictable behaviour between PTE scan updates,
+	 * background writeback, dirty balancing and application behaviour.
+	 */
+	if (!writable)
+		*flags |= TNF_NO_GROUP;
+
+	/*
+	 * Flag if the folio is shared between multiple address spaces. This
+	 * is later used when determining whether to group tasks together
+	 */
+	if (folio_maybe_mapped_shared(folio) && (vma->vm_flags & VM_SHARED))
+		*flags |= TNF_SHARED;
+	/*
+	 * For memory tiering mode, cpupid of slow memory page is used
+	 * to record page access time.  So use default value.
+	 */
+	if (folio_use_access_time(folio))
+		*last_cpupid = (-1 & LAST_CPUPID_MASK);
+	else
+		*last_cpupid = folio_last_cpupid(folio);
+
+	/* Record the current PID accessing VMA */
+	vma_set_access_pid_bit(vma);
+
+	count_vm_numa_event(NUMA_HINT_FAULTS);
+#ifdef CONFIG_NUMA_BALANCING
+	count_memcg_folio_events(folio, NUMA_HINT_FAULTS, 1);
+#endif
+	if (folio_nid(folio) == numa_node_id()) {
+		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
+		*flags |= TNF_FAULT_LOCAL;
+	}
+
+	return mpol_misplaced(folio, vmf, addr);
+}
+
+static void numa_rebuild_single_mapping(struct vm_fault *vmf, struct vm_area_struct *vma,
+					unsigned long fault_addr, pte_t *fault_pte,
+					bool writable)
+{
+	pte_t pte, old_pte;
+
+	old_pte = ptep_modify_prot_start(vma, fault_addr, fault_pte);
+	pte = pte_modify(old_pte, vma->vm_page_prot);
+	pte = pte_mkyoung(pte);
+	if (writable)
+		pte = pte_mkwrite(pte, vma);
+	ptep_modify_prot_commit(vma, fault_addr, fault_pte, old_pte, pte);
+	update_mmu_cache_range(vmf, vma, fault_addr, fault_pte, 1);
+}
+
+static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_struct *vma,
+				       struct folio *folio, pte_t fault_pte,
+				       bool ignore_writable, bool pte_write_upgrade)
+{
+	int nr = pte_pfn(fault_pte) - folio_pfn(folio);
+	unsigned long start, end, addr = vmf->address;
+	unsigned long addr_start = addr - (nr << PAGE_SHIFT);
+	unsigned long pt_start = ALIGN_DOWN(addr, PMD_SIZE);
+	pte_t *start_ptep;
+
+	/* Stay within the VMA and within the page table. */
+	start = max3(addr_start, pt_start, vma->vm_start);
+	end = min3(addr_start + folio_size(folio), pt_start + PMD_SIZE,
+		   vma->vm_end);
+	start_ptep = vmf->pte - ((addr - start) >> PAGE_SHIFT);
+
+	/* Restore all PTEs' mapping of the large folio */
+	for (addr = start; addr != end; start_ptep++, addr += PAGE_SIZE) {
+		pte_t ptent = ptep_get(start_ptep);
+		bool writable = false;
+
+		if (!pte_present(ptent) || !pte_protnone(ptent))
+			continue;
+
+		/*
+		 * RWP-armed PTEs are also protnone but carry _PAGE_UFFD as a
+		 * marker. Leave them alone -- rewriting to vm_page_prot would
+		 * stop the RWP trap. Gate on userfaultfd_rwp(vma) too:
+		 * NUMA balancing preserves _PAGE_UFFD on UFFD_WP-marked PTEs
+		 * when applying PROT_NONE, and those still need rebuilding.
+		 */
+		if (userfaultfd_rwp(vma) && pte_uffd(ptent))
+			continue;
+
+		if (pfn_folio(pte_pfn(ptent)) != folio)
+			continue;
+
+		if (!ignore_writable) {
+			ptent = pte_modify(ptent, vma->vm_page_prot);
+			writable = pte_write(ptent);
+			if (!writable && pte_write_upgrade &&
+			    can_change_pte_writable(vma, addr, ptent))
+				writable = true;
+		}
+
+		numa_rebuild_single_mapping(vmf, vma, addr, start_ptep, writable);
+	}
+}
+
+static vm_fault_t do_uffd_rwp(struct vm_fault *vmf)
+{
+	pte_t pte;
+
+	if (!userfaultfd_rwp_async(vmf->vma)) {
+		/* Sync mode: unmap PTE and deliver to userfaultfd handler */
+		pte_unmap(vmf->pte);
+		return handle_userfault(vmf, VM_UFFD_RWP);
+	}
+
+	spin_lock(vmf->ptl);
+	if (unlikely(!pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
+	}
+	pte = pte_modify(vmf->orig_pte, vmf->vma->vm_page_prot);
+	/* pte_modify() preserves _PAGE_UFFD; drop it on resolution */
+	pte = pte_clear_uffd(pte);
+	pte = pte_mkyoung(pte);
+	if (!pte_write(pte) &&
+	    vma_wants_manual_pte_write_upgrade(vmf->vma) &&
+	    can_change_pte_writable(vmf->vma, vmf->address, pte))
+		pte = pte_mkwrite(pte, vmf->vma);
+	set_pte_at(vmf->vma->vm_mm, vmf->address, vmf->pte, pte);
+	update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return 0;
+}
+
+static vm_fault_t do_numa_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio = NULL;
+	int nid = NUMA_NO_NODE;
+	bool writable = false, ignore_writable = false;
+	bool pte_write_upgrade = vma_wants_manual_pte_write_upgrade(vma);
+	int last_cpupid;
+	int target_nid;
+	pte_t pte, old_pte;
+	int flags = 0, nr_pages;
+
+	/*
+	 * The pte cannot be used safely until we verify, while holding the page
+	 * table lock, that its contents have not changed during fault handling.
+	 */
+	spin_lock(vmf->ptl);
+	/* Read the live PTE from the page tables: */
+	old_pte = ptep_get(vmf->pte);
+
+	if (unlikely(!pte_same(old_pte, vmf->orig_pte))) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
+	}
+
+	pte = pte_modify(old_pte, vma->vm_page_prot);
+
+	/*
+	 * Detect now whether the PTE could be writable; this information
+	 * is only valid while holding the PT lock.
+	 */
+	writable = pte_write(pte);
+	if (!writable && pte_write_upgrade &&
+	    can_change_pte_writable(vma, vmf->address, pte))
+		writable = true;
+
+	folio = vm_normal_folio(vma, vmf->address, pte);
+	if (!folio || folio_is_zone_device(folio))
+		goto out_map;
+
+	nid = folio_nid(folio);
+	nr_pages = folio_nr_pages(folio);
+
+	target_nid = numa_migrate_check(folio, vmf, vmf->address, &flags,
+					writable, &last_cpupid);
+	if (target_nid == NUMA_NO_NODE)
+		goto out_map;
+	if (migrate_misplaced_folio_prepare(folio, vma, target_nid)) {
+		flags |= TNF_MIGRATE_FAIL;
+		goto out_map;
+	}
+	/* The folio is isolated and isolation code holds a folio reference. */
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	writable = false;
+	ignore_writable = true;
+
+	/* Migrate to the requested node */
+	if (!migrate_misplaced_folio(folio, target_nid)) {
+		nid = target_nid;
+		flags |= TNF_MIGRATED;
+		task_numa_fault(last_cpupid, nid, nr_pages, flags);
+		return 0;
+	}
+
+	flags |= TNF_MIGRATE_FAIL;
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+				       vmf->address, &vmf->ptl);
+	if (unlikely(!vmf->pte))
+		return 0;
+	if (unlikely(!pte_same(ptep_get(vmf->pte), vmf->orig_pte))) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
+	}
+out_map:
+	/*
+	 * Make it present again, depending on how arch implements
+	 * non-accessible ptes, some can allow access by kernel mode.
+	 */
+	if (folio && folio_test_large(folio))
+		numa_rebuild_large_mapping(vmf, vma, folio, pte, ignore_writable,
+					   pte_write_upgrade);
+	else
+		numa_rebuild_single_mapping(vmf, vma, vmf->address, vmf->pte,
+					    writable);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+
+	if (nid != NUMA_NO_NODE)
+		task_numa_fault(last_cpupid, nid, nr_pages, flags);
+	return 0;
+}
+
+static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	if (vma_is_anonymous(vma))
+		return do_huge_pmd_anonymous_page(vmf);
+	if (vma->vm_ops->huge_fault)
+		return vma->vm_ops->huge_fault(vmf, PMD_ORDER);
+	return VM_FAULT_FALLBACK;
+}
+
+/* `inline' is required to avoid gcc 4.1.2 build error */
+static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
+	vm_fault_t ret;
+
+	if (vma_is_anonymous(vma)) {
+		if (likely(!unshare) &&
+		    userfaultfd_huge_pmd_wp(vma, vmf->orig_pmd)) {
+			if (userfaultfd_wp_async(vmf->vma))
+				goto split;
+			return handle_userfault(vmf, VM_UFFD_WP);
+		}
+		return do_huge_pmd_wp_page(vmf);
+	}
+
+	if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
+		if (vma->vm_ops->huge_fault) {
+			ret = vma->vm_ops->huge_fault(vmf, PMD_ORDER);
+			if (!(ret & VM_FAULT_FALLBACK))
+				return ret;
+		}
+	}
+
+split:
+	/* COW or write-notify handled on pte level: split pmd. */
+	__split_huge_pmd(vma, vmf->pmd, vmf->address, false);
+
+	return VM_FAULT_FALLBACK;
+}
+
+static vm_fault_t create_huge_pud(struct vm_fault *vmf)
+{
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) &&			\
+	defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+	struct vm_area_struct *vma = vmf->vma;
+	/* No support for anonymous transparent PUD pages yet */
+	if (vma_is_anonymous(vma))
+		return VM_FAULT_FALLBACK;
+	if (vma->vm_ops->huge_fault)
+		return vma->vm_ops->huge_fault(vmf, PUD_ORDER);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+	return VM_FAULT_FALLBACK;
+}
+
+static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
+{
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) &&			\
+	defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret;
+
+	/* No support for anonymous transparent PUD pages yet */
+	if (vma_is_anonymous(vma))
+		goto split;
+	if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
+		if (vma->vm_ops->huge_fault) {
+			ret = vma->vm_ops->huge_fault(vmf, PUD_ORDER);
+			if (!(ret & VM_FAULT_FALLBACK))
+				return ret;
+		}
+	}
+split:
+	/* COW or write-notify not handled on PUD level: split pud.*/
+	__split_huge_pud(vma, vmf->pud, vmf->address);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+	return VM_FAULT_FALLBACK;
+}
+
+/*
+ * The page faults may be spurious because of the racy access to the
+ * page table.  For example, a non-populated virtual page is accessed
+ * on 2 CPUs simultaneously, thus the page faults are triggered on
+ * both CPUs.  However, it's possible that one CPU (say CPU A) cannot
+ * find the reason for the page fault if the other CPU (say CPU B) has
+ * changed the page table before the PTE is checked on CPU A.  Most of
+ * the time, the spurious page faults can be ignored safely.  However,
+ * if the page fault is for the write access, it's possible that a
+ * stale read-only TLB entry exists in the local CPU and needs to be
+ * flushed on some architectures.  This is called the spurious page
+ * fault fixing.
+ *
+ * Note: flush_tlb_fix_spurious_fault() is defined as flush_tlb_page()
+ * by default and used as such on most architectures, while
+ * flush_tlb_fix_spurious_fault_pmd() is defined as NOP by default and
+ * used as such on most architectures.
+ */
+static void fix_spurious_fault(struct vm_fault *vmf,
+			       enum pgtable_level ptlevel)
+{
+	/* Skip spurious TLB flush for retried page fault */
+	if (vmf->flags & FAULT_FLAG_TRIED)
+		return;
+	/*
+	 * This is needed only for protection faults but the arch code
+	 * is not yet telling us if this is a protection fault or not.
+	 * This still avoids useless tlb flushes for .text page faults
+	 * with threads.
+	 */
+	if (vmf->flags & FAULT_FLAG_WRITE) {
+		if (ptlevel == PGTABLE_LEVEL_PTE)
+			flush_tlb_fix_spurious_fault(vmf->vma, vmf->address,
+						     vmf->pte);
+		else
+			flush_tlb_fix_spurious_fault_pmd(vmf->vma, vmf->address,
+							 vmf->pmd);
+	}
+}
+/*
+ * These routines also need to handle stuff like marking pages dirty
+ * and/or accessed for architectures that don't do it in hardware (most
+ * RISC architectures).  The early dirtying is also good on the i386.
+ *
+ * There is also a hook called "update_mmu_cache()" that architectures
+ * with external mmu caches can use to update those (ie the Sparc or
+ * PowerPC hashed page tables that act as extended TLBs).
+ *
+ * On entry, we hold either the VMA lock or the mmap_lock
+ * (see FAULT_FLAG_VMA_LOCK).
+ *
+ * The mmap_lock or VMA lock may have been released depending on flags
+ * and our return value.
+ * See filemap_fault() and __folio_lock_or_retry().
+ */
+static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
+{
+	pte_t entry;
+
+	if (unlikely(pmd_none(*vmf->pmd))) {
+		/*
+		 * Leave __pte_alloc() until later: because vm_ops->fault may
+		 * want to allocate huge page, and if we expose page table
+		 * for an instant, it will be difficult to retract from
+		 * concurrent faults and from rmap lookups.
+		 */
+		vmf->pte = NULL;
+		vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID;
+	} else {
+		pmd_t dummy_pmdval;
+
+		/*
+		 * A regular pmd is established and it can't morph into a huge
+		 * pmd by anon khugepaged, since that takes mmap_lock in write
+		 * mode; but shmem or file collapse to THP could still morph
+		 * it into a huge pmd: just retry later if so.
+		 *
+		 * Use the maywrite version to indicate that vmf->pte may be
+		 * modified, but since we will use pte_same() to detect the
+		 * change of the !pte_none() entry, there is no need to recheck
+		 * the pmdval. Here we choose to pass a dummy variable instead
+		 * of NULL, which helps new user think about why this place is
+		 * special.
+		 */
+		vmf->pte = pte_offset_map_rw_nolock(vmf->vma->vm_mm, vmf->pmd,
+						    vmf->address, &dummy_pmdval,
+						    &vmf->ptl);
+		if (unlikely(!vmf->pte))
+			return 0;
+		vmf->orig_pte = ptep_get_lockless(vmf->pte);
+		vmf->flags |= FAULT_FLAG_ORIG_PTE_VALID;
+
+		if (pte_none(vmf->orig_pte)) {
+			pte_unmap(vmf->pte);
+			vmf->pte = NULL;
+		}
+	}
+
+	if (!vmf->pte)
+		return do_pte_missing(vmf);
+
+	if (!pte_present(vmf->orig_pte))
+		return do_swap_page(vmf);
+
+	if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma)) {
+		/*
+		 * RWP-protected PTEs are protnone plus the uffd bit. On a
+		 * VM_UFFD_RWP VMA, a protnone PTE without the uffd bit is
+		 * NUMA hinting and must still fall through to do_numa_page().
+		 */
+		if (userfaultfd_pte_rwp(vmf->vma, vmf->orig_pte))
+			return do_uffd_rwp(vmf);
+		return do_numa_page(vmf);
+	}
+
+	spin_lock(vmf->ptl);
+	entry = vmf->orig_pte;
+	if (unlikely(!pte_same(ptep_get(vmf->pte), entry))) {
+		update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
+		goto unlock;
+	}
+	if (vmf->flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) {
+		if (!pte_write(entry))
+			return do_wp_page(vmf);
+		else if (likely(vmf->flags & FAULT_FLAG_WRITE))
+			entry = pte_mkdirty(entry);
+	}
+	entry = pte_mkyoung(entry);
+	if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
+				vmf->flags & FAULT_FLAG_WRITE))
+		update_mmu_cache_range(vmf, vmf->vma, vmf->address,
+				vmf->pte, 1);
+	else
+		fix_spurious_fault(vmf, PGTABLE_LEVEL_PTE);
+unlock:
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return 0;
+}
+
+/*
+ * On entry, we hold either the VMA lock or the mmap_lock
+ * (see FAULT_FLAG_VMA_LOCK).  If VM_FAULT_RETRY is set in
+ * the result, the lock is not held on exit.  See filemap_fault()
+ * and __folio_lock_or_retry().
+ */
+static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
+		unsigned long address, unsigned int flags)
+{
+	struct vm_fault vmf = {
+		.vma = vma,
+		.address = address & PAGE_MASK,
+		.real_address = address,
+		.flags = flags,
+		.pgoff = linear_page_index(vma, address),
+		.gfp_mask = __get_fault_gfp_mask(vma),
+	};
+	struct mm_struct *mm = vma->vm_mm;
+	vm_flags_t vm_flags = vma->vm_flags;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	vm_fault_t ret;
+
+	pgd = pgd_offset(mm, address);
+	p4d = p4d_alloc(mm, pgd, address);
+	if (!p4d)
+		return VM_FAULT_OOM;
+
+	vmf.pud = pud_alloc(mm, p4d, address);
+	if (!vmf.pud)
+		return VM_FAULT_OOM;
+retry_pud:
+	if (pud_none(*vmf.pud) &&
+	    thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PUD_ORDER)) {
+		ret = create_huge_pud(&vmf);
+		if (!(ret & VM_FAULT_FALLBACK))
+			return ret;
+	} else {
+		pud_t orig_pud = *vmf.pud;
+
+		barrier();
+		if (pud_trans_huge(orig_pud)) {
+
+			/*
+			 * TODO once we support anonymous PUDs: NUMA case and
+			 * FAULT_FLAG_UNSHARE handling.
+			 */
+			if ((flags & FAULT_FLAG_WRITE) && !pud_write(orig_pud)) {
+				ret = wp_huge_pud(&vmf, orig_pud);
+				if (!(ret & VM_FAULT_FALLBACK))
+					return ret;
+			} else {
+				huge_pud_set_accessed(&vmf, orig_pud);
+				return 0;
+			}
+		}
+	}
+
+	vmf.pmd = pmd_alloc(mm, vmf.pud, address);
+	if (!vmf.pmd)
+		return VM_FAULT_OOM;
+
+	/* Huge pud page fault raced with pmd_alloc? */
+	if (pud_trans_unstable(vmf.pud))
+		goto retry_pud;
+
+	if (pmd_none(*vmf.pmd) &&
+	    thp_vma_allowable_order(vma, vm_flags, TVA_PAGEFAULT, PMD_ORDER)) {
+		ret = create_huge_pmd(&vmf);
+		if (ret & VM_FAULT_FALLBACK)
+			goto fallback;
+		else
+			return ret;
+	}
+
+	vmf.orig_pmd = pmdp_get_lockless(vmf.pmd);
+	if (pmd_none(vmf.orig_pmd))
+		goto fallback;
+
+	if (unlikely(!pmd_present(vmf.orig_pmd))) {
+		if (pmd_is_device_private_entry(vmf.orig_pmd))
+			return do_huge_pmd_device_private(&vmf);
+
+		if (pmd_is_migration_entry(vmf.orig_pmd))
+			pmd_migration_entry_wait(mm, vmf.pmd);
+		return 0;
+	}
+	if (pmd_trans_huge(vmf.orig_pmd)) {
+		if (pmd_protnone(vmf.orig_pmd) && vma_is_accessible(vma)) {
+			if (userfaultfd_huge_pmd_rwp(vma, vmf.orig_pmd))
+				return do_huge_pmd_uffd_rwp(&vmf);
+			return do_huge_pmd_numa_page(&vmf);
+		}
+
+		if ((flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) &&
+		    !pmd_write(vmf.orig_pmd)) {
+			ret = wp_huge_pmd(&vmf);
+			if (!(ret & VM_FAULT_FALLBACK))
+				return ret;
+		} else {
+			vmf.ptl = pmd_lock(mm, vmf.pmd);
+			if (!huge_pmd_set_accessed(&vmf))
+				fix_spurious_fault(&vmf, PGTABLE_LEVEL_PMD);
+			spin_unlock(vmf.ptl);
+			return 0;
+		}
+	}
+
+fallback:
+	return handle_pte_fault(&vmf);
+}
+
+/**
+ * mm_account_fault - Do page fault accounting
+ * @mm: mm from which memcg should be extracted. It can be NULL.
+ * @regs: the pt_regs struct pointer.  When set to NULL, will skip accounting
+ *        of perf event counters, but we'll still do the per-task accounting to
+ *        the task who triggered this page fault.
+ * @address: the faulted address.
+ * @flags: the fault flags.
+ * @ret: the fault retcode.
+ *
+ * This will take care of most of the page fault accounting.  Meanwhile, it
+ * will also include the PERF_COUNT_SW_PAGE_FAULTS_[MAJ|MIN] perf counter
+ * updates.  However, note that the handling of PERF_COUNT_SW_PAGE_FAULTS should
+ * still be in per-arch page fault handlers at the entry of page fault.
+ */
+static inline void mm_account_fault(struct mm_struct *mm, struct pt_regs *regs,
+				    unsigned long address, unsigned int flags,
+				    vm_fault_t ret)
+{
+	bool major;
+
+	/* Incomplete faults will be accounted upon completion. */
+	if (ret & VM_FAULT_RETRY)
+		return;
+
+	/*
+	 * To preserve the behavior of older kernels, PGFAULT counters record
+	 * both successful and failed faults, as opposed to perf counters,
+	 * which ignore failed cases.
+	 */
+	count_vm_event(PGFAULT);
+	count_memcg_event_mm(mm, PGFAULT);
+
+	/*
+	 * Do not account for unsuccessful faults (e.g. when the address wasn't
+	 * valid).  That includes arch_vma_access_permitted() failing before
+	 * reaching here. So this is not a "this many hardware page faults"
+	 * counter.  We should use the hw profiling for that.
+	 */
+	if (ret & VM_FAULT_ERROR)
+		return;
+
+	/*
+	 * We define the fault as a major fault when the final successful fault
+	 * is VM_FAULT_MAJOR, or if it retried (which implies that we couldn't
+	 * handle it immediately previously).
+	 */
+	major = (ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED);
+
+	if (major)
+		current->maj_flt++;
+	else
+		current->min_flt++;
+
+	/*
+	 * If the fault is done for GUP, regs will be NULL.  We only do the
+	 * accounting for the per thread fault counters who triggered the
+	 * fault, and we skip the perf event updates.
+	 */
+	if (!regs)
+		return;
+
+	if (major)
+		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
+	else
+		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
+}
+
+#ifdef CONFIG_LRU_GEN
+static void lru_gen_enter_fault(struct vm_area_struct *vma)
+{
+	/* the LRU algorithm only applies to accesses with recency */
+	current->in_lru_fault = vma_has_recency(vma);
+}
+
+static void lru_gen_exit_fault(void)
+{
+	current->in_lru_fault = false;
+}
+#else
+static void lru_gen_enter_fault(struct vm_area_struct *vma)
+{
+}
+
+static void lru_gen_exit_fault(void)
+{
+}
+#endif /* CONFIG_LRU_GEN */
+
+static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
+				       unsigned int *flags)
+{
+	if (unlikely(*flags & FAULT_FLAG_UNSHARE)) {
+		if (WARN_ON_ONCE(*flags & FAULT_FLAG_WRITE))
+			return VM_FAULT_SIGSEGV;
+		/*
+		 * FAULT_FLAG_UNSHARE only applies to COW mappings. Let's
+		 * just treat it like an ordinary read-fault otherwise.
+		 */
+		if (!is_cow_mapping(vma->vm_flags))
+			*flags &= ~FAULT_FLAG_UNSHARE;
+	} else if (*flags & FAULT_FLAG_WRITE) {
+		/* Write faults on read-only mappings are impossible ... */
+		if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)))
+			return VM_FAULT_SIGSEGV;
+		/* ... and FOLL_FORCE only applies to COW mappings. */
+		if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) &&
+				 !is_cow_mapping(vma->vm_flags)))
+			return VM_FAULT_SIGSEGV;
+	}
+#ifdef CONFIG_PER_VMA_LOCK
+	/*
+	 * Per-VMA locks can't be used with FAULT_FLAG_RETRY_NOWAIT because of
+	 * the assumption that lock is dropped on VM_FAULT_RETRY.
+	 */
+	if (WARN_ON_ONCE((*flags &
+			(FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)) ==
+			(FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)))
+		return VM_FAULT_SIGSEGV;
+#endif
+
+	return 0;
+}
+
+/*
+ * By the time we get here, we already hold either the VMA lock or the
+ * mmap_lock (see FAULT_FLAG_VMA_LOCK).
+ *
+ * The lock may have been released depending on flags and our
+ * return value.  See filemap_fault() and __folio_lock_or_retry().
+ */
+vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
+			   unsigned int flags, struct pt_regs *regs)
+{
+	/* If the fault handler drops the mmap_lock, vma may be freed */
+	struct mm_struct *mm = vma->vm_mm;
+	vm_fault_t ret;
+	bool is_droppable;
+
+	__set_current_state(TASK_RUNNING);
+
+	ret = sanitize_fault_flags(vma, &flags);
+	if (ret)
+		goto out;
+
+	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+					    flags & FAULT_FLAG_INSTRUCTION,
+					    flags & FAULT_FLAG_REMOTE)) {
+		ret = VM_FAULT_SIGSEGV;
+		goto out;
+	}
+
+	is_droppable = !!(vma->vm_flags & VM_DROPPABLE);
+
+	/*
+	 * Enable the memcg OOM handling for faults triggered in user
+	 * space.  Kernel faults are handled more gracefully.
+	 */
+	if (flags & FAULT_FLAG_USER)
+		mem_cgroup_enter_user_fault();
+
+	lru_gen_enter_fault(vma);
+
+	if (unlikely(is_vm_hugetlb_page(vma)))
+		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
+	else
+		ret = __handle_mm_fault(vma, address, flags);
+
+	/*
+	 * Warning: It is no longer safe to dereference vma-> after this point,
+	 * because mmap_lock might have been dropped by __handle_mm_fault(), so
+	 * vma might be destroyed from underneath us.
+	 */
+
+	lru_gen_exit_fault();
+
+	/* If the mapping is droppable, then errors due to OOM aren't fatal. */
+	if (is_droppable)
+		ret &= ~VM_FAULT_OOM;
+
+	if (flags & FAULT_FLAG_USER) {
+		mem_cgroup_exit_user_fault();
+		/*
+		 * The task may have entered a memcg OOM situation but
+		 * if the allocation error was handled gracefully (no
+		 * VM_FAULT_OOM), there is no need to kill anything.
+		 * Just clean up the OOM state peacefully.
+		 */
+		if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
+			mem_cgroup_oom_synchronize(false);
+	}
+out:
+	mm_account_fault(mm, regs, address, flags, ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(handle_mm_fault);
+
+#ifndef __PAGETABLE_P4D_FOLDED
+/*
+ * Allocate p4d page table.
+ * We've already handled the fast-path in-line.
+ */
+int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
+{
+	p4d_t *new = p4d_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&mm->page_table_lock);
+	if (pgd_present(*pgd)) {	/* Another has populated it */
+		p4d_free(mm, new);
+	} else {
+		smp_wmb(); /* See comment in pmd_install() */
+		pgd_populate(mm, pgd, new);
+	}
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#endif /* __PAGETABLE_P4D_FOLDED */
+
+#ifndef __PAGETABLE_PUD_FOLDED
+/*
+ * Allocate page upper directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address)
+{
+	pud_t *new = pud_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&mm->page_table_lock);
+	if (!p4d_present(*p4d)) {
+		mm_inc_nr_puds(mm);
+		smp_wmb(); /* See comment in pmd_install() */
+		p4d_populate(mm, p4d, new);
+	} else	/* Another has populated it */
+		pud_free(mm, new);
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#endif /* __PAGETABLE_PUD_FOLDED */
+
+#ifndef __PAGETABLE_PMD_FOLDED
+/*
+ * Allocate page middle directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
+{
+	spinlock_t *ptl;
+	pmd_t *new = pmd_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	ptl = pud_lock(mm, pud);
+	if (!pud_present(*pud)) {
+		mm_inc_nr_pmds(mm);
+		smp_wmb(); /* See comment in pmd_install() */
+		pud_populate(mm, pud, new);
+	} else {	/* Another has populated it */
+		pmd_free(mm, new);
+	}
+	spin_unlock(ptl);
+	return 0;
+}
+#endif /* __PAGETABLE_PMD_FOLDED */
+
+static inline void pfnmap_args_setup(struct follow_pfnmap_args *args,
+				     spinlock_t *lock, pte_t *ptep,
+				     pgprot_t pgprot, unsigned long pfn_base,
+				     unsigned long addr_mask, bool writable,
+				     bool special)
+{
+	args->lock = lock;
+	args->ptep = ptep;
+	args->pfn = pfn_base + ((args->address & ~addr_mask) >> PAGE_SHIFT);
+	args->addr_mask = addr_mask;
+	args->pgprot = pgprot;
+	args->writable = writable;
+	args->special = special;
+}
+
+static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma)
+{
+#ifdef CONFIG_LOCKDEP
+	struct file *file = vma->vm_file;
+	struct address_space *mapping = file ? file->f_mapping : NULL;
+
+	if (mapping)
+		lockdep_assert(lockdep_is_held(&mapping->i_mmap_rwsem) ||
+			       lockdep_is_held(&vma->vm_mm->mmap_lock));
+	else
+		lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock));
+#endif
+}
+
+/**
+ * follow_pfnmap_start() - Look up a pfn mapping at a user virtual address
+ * @args: Pointer to struct @follow_pfnmap_args
+ *
+ * The caller needs to setup args->vma and args->address to point to the
+ * virtual address as the target of such lookup.  On a successful return,
+ * the results will be put into other output fields.
+ *
+ * After the caller finished using the fields, the caller must invoke
+ * another follow_pfnmap_end() to proper releases the locks and resources
+ * of such look up request.
+ *
+ * During the start() and end() calls, the results in @args will be valid
+ * as proper locks will be held.  After the end() is called, all the fields
+ * in @follow_pfnmap_args will be invalid to be further accessed.  Further
+ * use of such information after end() may require proper synchronizations
+ * by the caller with page table updates, otherwise it can create a
+ * security bug.
+ *
+ * If the PTE maps a refcounted page, callers are responsible to protect
+ * against invalidation with MMU notifiers; otherwise access to the PFN at
+ * a later point in time can trigger use-after-free.
+ *
+ * Only IO mappings and raw PFN mappings are allowed.  The mmap semaphore
+ * should be taken for read, and the mmap semaphore cannot be released
+ * before the end() is invoked.
+ *
+ * This function must not be used to modify PTE content.
+ *
+ * Return: zero on success, negative otherwise.
+ */
+int follow_pfnmap_start(struct follow_pfnmap_args *args)
+{
+	struct vm_area_struct *vma = args->vma;
+	unsigned long address = args->address;
+	struct mm_struct *mm = vma->vm_mm;
+	spinlock_t *lock;
+	pgd_t *pgdp;
+	p4d_t *p4dp, p4d;
+	pud_t *pudp, pud;
+	pmd_t *pmdp, pmd;
+	pte_t *ptep, pte;
+
+	pfnmap_lockdep_assert(vma);
+
+	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
+		goto out;
+
+	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		goto out;
+retry:
+	pgdp = pgd_offset(mm, address);
+	if (pgd_none(*pgdp) || unlikely(pgd_bad(*pgdp)))
+		goto out;
+
+	p4dp = p4d_offset(pgdp, address);
+	p4d = p4dp_get(p4dp);
+	if (p4d_none(p4d) || unlikely(p4d_bad(p4d)))
+		goto out;
+
+	pudp = pud_offset(p4dp, address);
+	pud = pudp_get(pudp);
+	if (!pud_present(pud))
+		goto out;
+	if (pud_leaf(pud)) {
+		lock = pud_lock(mm, pudp);
+		pud = pudp_get(pudp);
+
+		if (unlikely(!pud_present(pud))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pud_leaf(pud))) {
+			spin_unlock(lock);
+			goto retry;
+		}
+		pfnmap_args_setup(args, lock, NULL, pud_pgprot(pud),
+				  pud_pfn(pud), PUD_MASK, pud_write(pud),
+				  pud_special(pud));
+		return 0;
+	}
+
+	pmdp = pmd_offset(pudp, address);
+	pmd = pmdp_get_lockless(pmdp);
+	if (!pmd_present(pmd))
+		goto out;
+	if (pmd_leaf(pmd)) {
+		lock = pmd_lock(mm, pmdp);
+		pmd = pmdp_get(pmdp);
+
+		if (unlikely(!pmd_present(pmd))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pmd_leaf(pmd))) {
+			spin_unlock(lock);
+			goto retry;
+		}
+		pfnmap_args_setup(args, lock, NULL, pmd_pgprot(pmd),
+				  pmd_pfn(pmd), PMD_MASK, pmd_write(pmd),
+				  pmd_special(pmd));
+		return 0;
+	}
+
+	ptep = pte_offset_map_lock(mm, pmdp, address, &lock);
+	if (!ptep)
+		goto out;
+	pte = ptep_get(ptep);
+	if (!pte_present(pte))
+		goto unlock;
+	pfnmap_args_setup(args, lock, ptep, pte_pgprot(pte),
+			  pte_pfn(pte), PAGE_MASK, pte_write(pte),
+			  pte_special(pte));
+	return 0;
+unlock:
+	pte_unmap_unlock(ptep, lock);
+out:
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(follow_pfnmap_start);
+
+/**
+ * follow_pfnmap_end(): End a follow_pfnmap_start() process
+ * @args: Pointer to struct @follow_pfnmap_args
+ *
+ * Must be used in pair of follow_pfnmap_start().  See the start() function
+ * above for more information.
+ */
+void follow_pfnmap_end(struct follow_pfnmap_args *args)
+{
+	if (args->lock)
+		spin_unlock(args->lock);
+	if (args->ptep)
+		pte_unmap(args->ptep);
+}
+EXPORT_SYMBOL_GPL(follow_pfnmap_end);
+
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+/**
+ * generic_access_phys - generic implementation for iomem mmap access
+ * @vma: the vma to access
+ * @addr: userspace address, not relative offset within @vma
+ * @buf: buffer to read/write
+ * @len: length of transfer
+ * @write: set to FOLL_WRITE when writing, otherwise reading
+ *
+ * This is a generic implementation for &vm_operations_struct.access for an
+ * iomem mapping. This callback is used by access_process_vm() when the @vma is
+ * not page based.
+ */
+int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
+			void *buf, int len, int write)
+{
+	resource_size_t phys_addr;
+	pgprot_t prot = __pgprot(0);
+	void __iomem *maddr;
+	int offset = offset_in_page(addr);
+	int ret = -EINVAL;
+	bool writable;
+	struct follow_pfnmap_args args = { .vma = vma, .address = addr };
+
+retry:
+	if (follow_pfnmap_start(&args))
+		return -EINVAL;
+	prot = args.pgprot;
+	phys_addr = (resource_size_t)args.pfn << PAGE_SHIFT;
+	writable = args.writable;
+	follow_pfnmap_end(&args);
+
+	if ((write & FOLL_WRITE) && !writable)
+		return -EINVAL;
+
+	maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot);
+	if (!maddr)
+		return -ENOMEM;
+
+	if (follow_pfnmap_start(&args))
+		goto out_unmap;
+
+	if ((pgprot_val(prot) != pgprot_val(args.pgprot)) ||
+	    (phys_addr != (args.pfn << PAGE_SHIFT)) ||
+	    (writable != args.writable)) {
+		follow_pfnmap_end(&args);
+		iounmap(maddr);
+		goto retry;
+	}
+
+	if (write)
+		memcpy_toio(maddr + offset, buf, len);
+	else
+		memcpy_fromio(buf, maddr + offset, len);
+	ret = len;
+	follow_pfnmap_end(&args);
+out_unmap:
+	iounmap(maddr);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(generic_access_phys);
+#endif
+
+/*
+ * Access another process' address space as given in mm.
+ */
+static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
+			      void *buf, int len, unsigned int gup_flags)
+{
+	void *old_buf = buf;
+	int write = gup_flags & FOLL_WRITE;
+
+	if (mmap_read_lock_killable(mm))
+		return 0;
+
+	/* Untag the address before looking up the VMA */
+	addr = untagged_addr_remote(mm, addr);
+
+	/* Avoid triggering the temporary warning in __get_user_pages */
+	if (!vma_lookup(mm, addr) && !expand_stack(mm, addr))
+		return 0;
+
+	/* ignore errors, just check how much was successfully transferred */
+	while (len) {
+		int bytes, offset;
+		void *maddr;
+		struct folio *folio;
+		struct vm_area_struct *vma = NULL;
+		struct page *page = get_user_page_vma_remote(mm, addr,
+							     gup_flags, &vma);
+
+		if (IS_ERR(page)) {
+			/* We might need to expand the stack to access it */
+			vma = vma_lookup(mm, addr);
+			if (!vma) {
+				vma = expand_stack(mm, addr);
+
+				/* mmap_lock was dropped on failure */
+				if (!vma)
+					return buf - old_buf;
+
+				/* Try again if stack expansion worked */
+				continue;
+			}
+
+			/*
+			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
+			 * we can access using slightly different code.
+			 */
+			bytes = 0;
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+			if (vma->vm_ops && vma->vm_ops->access)
+				bytes = vma->vm_ops->access(vma, addr, buf,
+							    len, write);
+#endif
+			if (bytes <= 0)
+				break;
+		} else {
+			folio = page_folio(page);
+			bytes = len;
+			offset = addr & (PAGE_SIZE-1);
+			if (bytes > PAGE_SIZE-offset)
+				bytes = PAGE_SIZE-offset;
+
+			maddr = kmap_local_folio(folio, folio_page_idx(folio, page) * PAGE_SIZE);
+			if (write) {
+				copy_to_user_page(vma, page, addr,
+						  maddr + offset, buf, bytes);
+				folio_mark_dirty_lock(folio);
+			} else {
+				copy_from_user_page(vma, page, addr,
+						    buf, maddr + offset, bytes);
+			}
+			folio_release_kmap(folio, maddr);
+		}
+		len -= bytes;
+		buf += bytes;
+		addr += bytes;
+	}
+	mmap_read_unlock(mm);
+
+	return buf - old_buf;
+}
+
+/**
+ * access_remote_vm - access another process' address space
+ * @mm:		the mm_struct of the target address space
+ * @addr:	start address to access
+ * @buf:	source or destination buffer
+ * @len:	number of bytes to transfer
+ * @gup_flags:	flags modifying lookup behaviour
+ *
+ * The caller must hold a reference on @mm.
+ *
+ * Return: number of bytes copied from source to destination.
+ */
+int access_remote_vm(struct mm_struct *mm, unsigned long addr,
+		void *buf, int len, unsigned int gup_flags)
+{
+	return __access_remote_vm(mm, addr, buf, len, gup_flags);
+}
+
+/*
+ * Access another process' address space.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr,
+		void *buf, int len, unsigned int gup_flags)
+{
+	struct mm_struct *mm;
+	int ret;
+
+	mm = get_task_mm(tsk);
+	if (!mm)
+		return 0;
+
+	ret = __access_remote_vm(mm, addr, buf, len, gup_flags);
+
+	mmput(mm);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(access_process_vm);
+
+#ifdef CONFIG_BPF_SYSCALL
+/*
+ * Copy a string from another process's address space as given in mm.
+ * If there is any error return -EFAULT.
+ */
+static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
+				void *buf, int len, unsigned int gup_flags)
+{
+	void *old_buf = buf;
+	int err = 0;
+
+	*(char *)buf = '\0';
+
+	if (mmap_read_lock_killable(mm))
+		return -EFAULT;
+
+	addr = untagged_addr_remote(mm, addr);
+
+	/* Avoid triggering the temporary warning in __get_user_pages */
+	if (!vma_lookup(mm, addr)) {
+		err = -EFAULT;
+		goto out;
+	}
+
+	while (len) {
+		int bytes, offset, retval;
+		void *maddr;
+		struct folio *folio;
+		struct page *page;
+		struct vm_area_struct *vma = NULL;
+
+		page = get_user_page_vma_remote(mm, addr, gup_flags, &vma);
+		if (IS_ERR(page)) {
+			/*
+			 * Treat as a total failure for now until we decide how
+			 * to handle the CONFIG_HAVE_IOREMAP_PROT case and
+			 * stack expansion.
+			 */
+			*(char *)buf = '\0';
+			err = -EFAULT;
+			goto out;
+		}
+
+		folio = page_folio(page);
+		bytes = len;
+		offset = addr & (PAGE_SIZE - 1);
+		if (bytes > PAGE_SIZE - offset)
+			bytes = PAGE_SIZE - offset;
+
+		maddr = kmap_local_folio(folio, folio_page_idx(folio, page) * PAGE_SIZE);
+		retval = strscpy(buf, maddr + offset, bytes);
+		if (retval >= 0) {
+			/* Found the end of the string */
+			buf += retval;
+			folio_release_kmap(folio, maddr);
+			break;
+		}
+
+		buf += bytes - 1;
+		/*
+		 * Because strscpy always NUL terminates we need to
+		 * copy the last byte in the page if we are going to
+		 * load more pages
+		 */
+		if (bytes != len) {
+			addr += bytes - 1;
+			copy_from_user_page(vma, page, addr, buf, maddr + (PAGE_SIZE - 1), 1);
+			buf += 1;
+			addr += 1;
+		}
+		len -= bytes;
+
+		folio_release_kmap(folio, maddr);
+	}
+
+out:
+	mmap_read_unlock(mm);
+	if (err)
+		return err;
+	return buf - old_buf;
+}
+
+/**
+ * copy_remote_vm_str - copy a string from another process's address space.
+ * @tsk:	the task of the target address space
+ * @addr:	start address to read from
+ * @buf:	destination buffer
+ * @len:	number of bytes to copy
+ * @gup_flags:	flags modifying lookup behaviour
+ *
+ * The caller must hold a reference on @mm.
+ *
+ * Return: number of bytes copied from @addr (source) to @buf (destination);
+ * not including the trailing NUL. Always guaranteed to leave NUL-terminated
+ * buffer. On any error, return -EFAULT.
+ */
+int copy_remote_vm_str(struct task_struct *tsk, unsigned long addr,
+		       void *buf, int len, unsigned int gup_flags)
+{
+	struct mm_struct *mm;
+	int ret;
+
+	if (unlikely(len == 0))
+		return 0;
+
+	mm = get_task_mm(tsk);
+	if (!mm) {
+		*(char *)buf = '\0';
+		return -EFAULT;
+	}
+
+	ret = __copy_remote_vm_str(mm, addr, buf, len, gup_flags);
+
+	mmput(mm);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(copy_remote_vm_str);
+#endif /* CONFIG_BPF_SYSCALL */
+
+/*
+ * Print the name of a VMA.
+ */
+void print_vma_addr(char *prefix, unsigned long ip)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+
+	/*
+	 * we might be running from an atomic context so we cannot sleep
+	 */
+	if (!mmap_read_trylock(mm))
+		return;
+
+	vma = vma_lookup(mm, ip);
+	if (vma && vma->vm_file) {
+		struct file *f = vma->vm_file;
+		ip -= vma->vm_start;
+		ip += vma_start_pgoff(vma) << PAGE_SHIFT;
+		printk("%s%pD[%lx,%lx+%lx]", prefix, f, ip,
+				vma->vm_start,
+				vma->vm_end - vma->vm_start);
+	}
+	mmap_read_unlock(mm);
+}
+
+#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
+void __might_fault(const char *file, int line)
+{
+	if (pagefault_disabled())
+		return;
+	__might_sleep(file, line);
+	if (current->mm)
+		might_lock_read(&current->mm->mmap_lock);
+}
+EXPORT_SYMBOL(__might_fault);
+#endif
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
+/*
+ * Process all subpages of the specified huge page with the specified
+ * operation.  The target subpage will be processed last to keep its
+ * cache lines hot.
+ */
+static inline int process_huge_page(
+	unsigned long addr_hint, unsigned int nr_pages,
+	int (*process_subpage)(unsigned long addr, int idx, void *arg),
+	void *arg)
+{
+	int i, n, base, l, ret;
+	unsigned long addr = addr_hint &
+		~(((unsigned long)nr_pages << PAGE_SHIFT) - 1);
+
+	/* Process target subpage last to keep its cache lines hot */
+	might_sleep();
+	n = (addr_hint - addr) / PAGE_SIZE;
+	if (2 * n <= nr_pages) {
+		/* If target subpage in first half of huge page */
+		base = 0;
+		l = n;
+		/* Process subpages at the end of huge page */
+		for (i = nr_pages - 1; i >= 2 * n; i--) {
+			cond_resched();
+			ret = process_subpage(addr + i * PAGE_SIZE, i, arg);
+			if (ret)
+				return ret;
+		}
+	} else {
+		/* If target subpage in second half of huge page */
+		base = nr_pages - 2 * (nr_pages - n);
+		l = nr_pages - n;
+		/* Process subpages at the begin of huge page */
+		for (i = 0; i < base; i++) {
+			cond_resched();
+			ret = process_subpage(addr + i * PAGE_SIZE, i, arg);
+			if (ret)
+				return ret;
+		}
+	}
+	/*
+	 * Process remaining subpages in left-right-left-right pattern
+	 * towards the target subpage
+	 */
+	for (i = 0; i < l; i++) {
+		int left_idx = base + i;
+		int right_idx = base + 2 * l - 1 - i;
+
+		cond_resched();
+		ret = process_subpage(addr + left_idx * PAGE_SIZE, left_idx, arg);
+		if (ret)
+			return ret;
+		cond_resched();
+		ret = process_subpage(addr + right_idx * PAGE_SIZE, right_idx, arg);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
+static void clear_contig_highpages(struct page *page, unsigned long addr,
+				   unsigned int nr_pages)
+{
+	unsigned int i, count;
+	/*
+	 * When clearing we want to operate on the largest extent possible to
+	 * allow for architecture specific extent based optimizations.
+	 *
+	 * However, since clear_user_highpages() (and primitives clear_user_pages(),
+	 * clear_pages()), do not call cond_resched(), limit the unit size when
+	 * running under non-preemptible scheduling models.
+	 */
+	const unsigned int unit = preempt_model_preemptible() ?
+				   nr_pages : PROCESS_PAGES_NON_PREEMPT_BATCH;
+
+	might_sleep();
+
+	for (i = 0; i < nr_pages; i += count) {
+		cond_resched();
+
+		count = min(unit, nr_pages - i);
+		clear_user_highpages(page + i, addr + i * PAGE_SIZE, count);
+	}
+}
+
+/*
+ * When zeroing a folio, we want to differentiate between pages in the
+ * vicinity of the faulting address where we have spatial and temporal
+ * locality, and those far away where we don't.
+ *
+ * Use a radius of 2 for determining the local neighbourhood.
+ */
+#define FOLIO_ZERO_LOCALITY_RADIUS	2
+
+/**
+ * folio_zero_user - Zero a folio which will be mapped to userspace.
+ * @folio: The folio to zero.
+ * @addr_hint: The address accessed by the user or the base address.
+ */
+void folio_zero_user(struct folio *folio, unsigned long addr_hint)
+{
+	const unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio));
+	const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE;
+	const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);
+	const long radius = FOLIO_ZERO_LOCALITY_RADIUS;
+	struct range r[3];
+	int i;
+
+	/*
+	 * Faulting page and its immediate neighbourhood. Will be cleared at the
+	 * end to keep its cachelines hot.
+	 */
+	r[2] = DEFINE_RANGE(fault_idx - radius < (long)pg.start ? pg.start : fault_idx - radius,
+			    fault_idx + radius > (long)pg.end   ? pg.end   : fault_idx + radius);
+
+
+	/* Region to the left of the fault */
+	r[1] = DEFINE_RANGE(pg.start, r[2].start - 1);
+
+	/* Region to the right of the fault: always valid for the common fault_idx=0 case. */
+	r[0] = DEFINE_RANGE(r[2].end + 1, pg.end);
+
+	for (i = 0; i < ARRAY_SIZE(r); i++) {
+		const unsigned long addr = base_addr + r[i].start * PAGE_SIZE;
+		const long nr_pages = (long)range_len(&r[i]);
+		struct page *page = folio_page(folio, r[i].start);
+
+		if (nr_pages > 0)
+			clear_contig_highpages(page, addr, nr_pages);
+	}
+}
+
+static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
+				   unsigned long addr_hint,
+				   struct vm_area_struct *vma,
+				   unsigned int nr_pages)
+{
+	unsigned long addr = ALIGN_DOWN(addr_hint, folio_size(dst));
+	struct page *dst_page;
+	struct page *src_page;
+	int i;
+
+	for (i = 0; i < nr_pages; i++) {
+		dst_page = folio_page(dst, i);
+		src_page = folio_page(src, i);
+
+		cond_resched();
+		if (copy_mc_user_highpage(dst_page, src_page,
+					  addr + i*PAGE_SIZE, vma))
+			return -EHWPOISON;
+	}
+	return 0;
+}
+
+struct copy_subpage_arg {
+	struct folio *dst;
+	struct folio *src;
+	struct vm_area_struct *vma;
+};
+
+static int copy_subpage(unsigned long addr, int idx, void *arg)
+{
+	struct copy_subpage_arg *copy_arg = arg;
+	struct page *dst = folio_page(copy_arg->dst, idx);
+	struct page *src = folio_page(copy_arg->src, idx);
+
+	if (copy_mc_user_highpage(dst, src, addr, copy_arg->vma))
+		return -EHWPOISON;
+	return 0;
+}
+
+int copy_user_large_folio(struct folio *dst, struct folio *src,
+			  unsigned long addr_hint, struct vm_area_struct *vma)
+{
+	unsigned int nr_pages = folio_nr_pages(dst);
+	struct copy_subpage_arg arg = {
+		.dst = dst,
+		.src = src,
+		.vma = vma,
+	};
+
+	if (unlikely(nr_pages > MAX_ORDER_NR_PAGES))
+		return copy_user_gigantic_page(dst, src, addr_hint, vma, nr_pages);
+
+	return process_huge_page(addr_hint, nr_pages, copy_subpage, &arg);
+}
+
+long copy_folio_from_user(struct folio *dst_folio,
+			   const void __user *usr_src,
+			   bool allow_pagefault)
+{
+	void *kaddr;
+	unsigned long i, rc = 0;
+	unsigned int nr_pages = folio_nr_pages(dst_folio);
+	unsigned long ret_val = nr_pages * PAGE_SIZE;
+	struct page *subpage;
+
+	for (i = 0; i < nr_pages; i++) {
+		subpage = folio_page(dst_folio, i);
+		kaddr = kmap_local_page(subpage);
+		if (!allow_pagefault)
+			pagefault_disable();
+		rc = copy_from_user(kaddr, usr_src + i * PAGE_SIZE, PAGE_SIZE);
+		if (!allow_pagefault)
+			pagefault_enable();
+		kunmap_local(kaddr);
+
+		ret_val -= (PAGE_SIZE - rc);
+		if (rc)
+			break;
+
+		flush_dcache_page(subpage);
+
+		cond_resched();
+	}
+	return ret_val;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
+
+#if defined(CONFIG_SPLIT_PTE_PTLOCKS) && ALLOC_SPLIT_PTLOCKS
+
+static struct kmem_cache *page_ptl_cachep;
+
+void __init ptlock_cache_init(void)
+{
+	page_ptl_cachep = kmem_cache_create("page->ptl", sizeof(spinlock_t), 0,
+			SLAB_PANIC, NULL);
+}
+
+bool ptlock_alloc(struct ptdesc *ptdesc)
+{
+	spinlock_t *ptl;
+
+	ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
+	if (!ptl)
+		return false;
+	ptdesc->ptl = ptl;
+	return true;
+}
+
+void ptlock_free(struct ptdesc *ptdesc)
+{
+	if (ptdesc->ptl)
+		kmem_cache_free(page_ptl_cachep, ptdesc->ptl);
+}
+#endif
+
+void vma_pgtable_walk_begin(struct vm_area_struct *vma)
+{
+	if (is_vm_hugetlb_page(vma))
+		hugetlb_vma_lock_read(vma);
+}
+
+void vma_pgtable_walk_end(struct vm_area_struct *vma)
+{
+	if (is_vm_hugetlb_page(vma))
+		hugetlb_vma_unlock_read(vma);
+}