sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 366 insertions, 0 deletions

diff --git a/mm/secretmem.c b/mm/secretmem.c
new file mode 100644
index 000000000..384f5cfc4
--- /dev/null
+++ b/mm/secretmem.c
@@ -0,0 +1,366 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright IBM Corporation, 2021
+ *
+ * Author: Mike Rapoport <rppt@linux.ibm.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/swap.h>
+#include <linux/mount.h>
+#include <linux/memfd.h>
+#include <linux/bitops.h>
+#include <linux/printk.h>
+#include <linux/pagemap.h>
+#include <linux/syscalls.h>
+#include <linux/pseudo_fs.h>
+#include <linux/secretmem.h>
+#include <linux/set_memory.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/user.h>
+#include <linux/cred.h>
+
+#include <uapi/linux/magic.h>
+
+#include <asm/tlbflush.h>
+
+#include "internal.h"
+
+#undef pr_fmt
+#define pr_fmt(fmt) "secretmem: " fmt
+
+/*
+ * Define mode and flag masks to allow validation of the system call
+ * parameters.
+ */
+#define SECRETMEM_MODE_MASK	(0x0)
+#define SECRETMEM_FLAGS_MASK	SECRETMEM_MODE_MASK
+
+static bool secretmem_enable __ro_after_init = 1;
+module_param_named(enable, secretmem_enable, bool, 0400);
+MODULE_PARM_DESC(secretmem_enable,
+		 "Enable secretmem and memfd_secret(2) system call");
+
+static atomic_t secretmem_users;
+
+bool secretmem_active(void)
+{
+	return !!atomic_read(&secretmem_users);
+}
+
+struct secretmem_inode_state {
+	struct user_struct	*user;
+	atomic_long_t		nr_pages_accounted;
+};
+
+static bool __secretmem_account_pages(struct user_struct *user,
+		unsigned long nr_pages)
+{
+	unsigned long page_limit, cur_pages, new_pages;
+
+	if (!nr_pages)
+		return true;
+
+	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+	cur_pages = atomic_long_read(&user->locked_vm);
+	do {
+		new_pages = cur_pages + nr_pages;
+		if (new_pages > page_limit)
+			return false;
+	} while (!atomic_long_try_cmpxchg(&user->locked_vm,
+					  &cur_pages, new_pages));
+	return true;
+}
+
+static bool secretmem_account_folio(struct secretmem_inode_state *state,
+		const struct folio *folio)
+{
+	const unsigned long nr_pages = folio_nr_pages(folio);
+
+	if (!__secretmem_account_pages(state->user, nr_pages))
+		return false;
+
+	atomic_long_add(nr_pages, &state->nr_pages_accounted);
+	return true;
+}
+
+static void __secretmem_unaccount_pages(struct secretmem_inode_state *state,
+		unsigned long nr_pages)
+{
+	atomic_long_sub(nr_pages, &state->user->locked_vm);
+	atomic_long_sub(nr_pages, &state->nr_pages_accounted);
+}
+
+static void secretmem_unaccount_folio(struct secretmem_inode_state *state,
+		struct folio *folio)
+{
+	__secretmem_unaccount_pages(state, folio_nr_pages(folio));
+}
+
+static void secretmem_unaccount_all_folios(struct secretmem_inode_state *state)
+{
+	const unsigned long nr_pages_accounted =
+		atomic_long_read(&state->nr_pages_accounted);
+
+	__secretmem_unaccount_pages(state, nr_pages_accounted);
+}
+
+static vm_fault_t secretmem_fault(struct vm_fault *vmf)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct secretmem_inode_state *state = inode->i_private;
+	pgoff_t offset = vmf->pgoff;
+	gfp_t gfp = vmf->gfp_mask;
+	unsigned long addr;
+	struct folio *folio;
+	vm_fault_t ret;
+	int err;
+
+	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
+		return vmf_error(-EINVAL);
+
+	filemap_invalidate_lock_shared(mapping);
+
+retry:
+	folio = filemap_lock_folio(mapping, offset);
+	if (IS_ERR(folio)) {
+		folio = folio_alloc(gfp | __GFP_ZERO, 0);
+		if (!folio) {
+			ret = VM_FAULT_OOM;
+			goto out;
+		}
+
+		if (!secretmem_account_folio(state, folio)) {
+			folio_put(folio);
+			ret = VM_FAULT_SIGBUS;
+			goto out;
+		}
+
+		err = set_direct_map_invalid_noflush(folio_page(folio, 0));
+		if (err) {
+			secretmem_unaccount_folio(state, folio);
+			folio_put(folio);
+			ret = vmf_error(err);
+			goto out;
+		}
+
+		__folio_mark_uptodate(folio);
+		err = filemap_add_folio(mapping, folio, offset, gfp);
+		if (unlikely(err)) {
+			secretmem_unaccount_folio(state, folio);
+			/*
+			 * If a split of large page was required, it
+			 * already happened when we marked the page invalid
+			 * which guarantees that this call won't fail
+			 */
+			set_direct_map_default_noflush(folio_page(folio, 0));
+			folio_put(folio);
+			if (err == -EEXIST)
+				goto retry;
+
+			ret = vmf_error(err);
+			goto out;
+		}
+
+		addr = (unsigned long)folio_address(folio);
+		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+	}
+
+	vmf->page = folio_file_page(folio, vmf->pgoff);
+	ret = VM_FAULT_LOCKED;
+
+out:
+	filemap_invalidate_unlock_shared(mapping);
+	return ret;
+}
+
+static const struct vm_operations_struct secretmem_vm_ops = {
+	.fault = secretmem_fault,
+};
+
+static void secretmem_destroy_inode_priv(struct inode *inode)
+{
+	struct secretmem_inode_state *state = inode->i_private;
+
+	secretmem_unaccount_all_folios(state);
+	free_uid(state->user);
+	kfree(state);
+	inode->i_private = NULL;
+}
+
+static int secretmem_release(struct inode *inode, struct file *file)
+{
+	atomic_dec(&secretmem_users);
+	secretmem_destroy_inode_priv(inode);
+
+	return 0;
+}
+
+static int secretmem_mmap_prepare(struct vm_area_desc *desc)
+{
+	if (!vma_desc_test_any(desc, VMA_SHARED_BIT, VMA_MAYSHARE_BIT))
+		return -EINVAL;
+
+	vma_desc_set_flags(desc, VMA_DONTDUMP_BIT);
+	desc->vm_ops = &secretmem_vm_ops;
+
+	return 0;
+}
+
+bool vma_is_secretmem(struct vm_area_struct *vma)
+{
+	return vma->vm_ops == &secretmem_vm_ops;
+}
+
+static const struct file_operations secretmem_fops = {
+	.release	= secretmem_release,
+	.mmap_prepare	= secretmem_mmap_prepare,
+};
+
+static int secretmem_migrate_folio(struct address_space *mapping,
+		struct folio *dst, struct folio *src, enum migrate_mode mode)
+{
+	return -EBUSY;
+}
+
+static void secretmem_free_folio(struct folio *folio)
+{
+	set_direct_map_default_noflush(folio_page(folio, 0));
+	folio_zero_segment(folio, 0, folio_size(folio));
+}
+
+const struct address_space_operations secretmem_aops = {
+	.dirty_folio	= noop_dirty_folio,
+	.free_folio	= secretmem_free_folio,
+	.migrate_folio	= secretmem_migrate_folio,
+};
+
+static int secretmem_setattr(struct mnt_idmap *idmap,
+			     struct dentry *dentry, struct iattr *iattr)
+{
+	struct inode *inode = d_inode(dentry);
+	struct address_space *mapping = inode->i_mapping;
+	unsigned int ia_valid = iattr->ia_valid;
+	int ret;
+
+	filemap_invalidate_lock(mapping);
+
+	if ((ia_valid & ATTR_SIZE) && inode->i_size)
+		ret = -EINVAL;
+	else
+		ret = simple_setattr(idmap, dentry, iattr);
+
+	filemap_invalidate_unlock(mapping);
+
+	return ret;
+}
+
+static const struct inode_operations secretmem_iops = {
+	.setattr = secretmem_setattr,
+};
+
+static struct vfsmount *secretmem_mnt;
+
+static int secretmem_init_inode_priv(struct inode *inode)
+{
+	struct secretmem_inode_state *state;
+
+	state = kzalloc_obj(*state);
+	if (!state)
+		return -ENOMEM;
+
+	state->user = get_uid(current_user());
+	inode->i_private = state;
+	return 0;
+}
+
+static struct file *secretmem_file_create(unsigned long flags)
+{
+	struct file *file;
+	struct inode *inode;
+	const char *anon_name = "[secretmem]";
+	int err;
+
+	inode = anon_inode_make_secure_inode(secretmem_mnt->mnt_sb, anon_name, NULL);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	err = secretmem_init_inode_priv(inode);
+	if (err)
+		goto err_free_inode;
+
+	file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
+				 O_RDWR | O_LARGEFILE, &secretmem_fops);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_free_priv;
+	}
+
+	mapping_set_gfp_mask(inode->i_mapping, GFP_USER);
+	mapping_set_unevictable(inode->i_mapping);
+
+	inode->i_op = &secretmem_iops;
+	inode->i_mapping->a_ops = &secretmem_aops;
+
+	/* pretend we are a normal file with zero size */
+	inode->i_mode |= S_IFREG;
+	inode->i_size = 0;
+
+	atomic_inc(&secretmem_users);
+
+	return file;
+err_free_priv:
+	secretmem_destroy_inode_priv(inode);
+err_free_inode:
+	iput(inode);
+	return ERR_PTR(err);
+}
+
+SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
+{
+	/* make sure local flags do not conflict with global fcntl.h */
+	BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
+
+	if (!secretmem_enable || !can_set_direct_map())
+		return -ENOSYS;
+
+	if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
+		return -EINVAL;
+	if (atomic_read(&secretmem_users) < 0)
+		return -ENFILE;
+
+	return FD_ADD(flags & O_CLOEXEC, secretmem_file_create(flags));
+}
+
+static int secretmem_init_fs_context(struct fs_context *fc)
+{
+	struct pseudo_fs_context *ctx;
+
+	ctx = init_pseudo(fc, SECRETMEM_MAGIC);
+	if (!ctx)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static struct file_system_type secretmem_fs = {
+	.name		= "secretmem",
+	.init_fs_context = secretmem_init_fs_context,
+	.kill_sb	= kill_anon_super,
+};
+
+static int __init secretmem_init(void)
+{
+	if (!secretmem_enable || !can_set_direct_map())
+		return 0;
+
+	secretmem_mnt = kern_mount(&secretmem_fs);
+	if (IS_ERR(secretmem_mnt))
+		return PTR_ERR(secretmem_mnt);
+
+	return 0;
+}
+fs_initcall(secretmem_init);