KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 256 insertions, 0 deletions

diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
new file mode 100644
index 000000000..16e11b6f6
--- /dev/null
+++ b/arch/xtensa/mm/fault.c
@@ -0,0 +1,256 @@
+// TODO VM_EXEC flag work-around, cache aliasing
+/*
+ * arch/xtensa/mm/fault.c
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2001 - 2010 Tensilica Inc.
+ *
+ * Chris Zankel <chris@zankel.net>
+ * Joe Taylor	<joe@tensilica.com, joetylr@yahoo.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/extable.h>
+#include <linux/hardirq.h>
+#include <linux/perf_event.h>
+#include <linux/uaccess.h>
+#include <asm/mmu_context.h>
+#include <asm/cacheflush.h>
+#include <asm/hardirq.h>
+#include <asm/traps.h>
+
+void bad_page_fault(struct pt_regs*, unsigned long, int);
+
+static void vmalloc_fault(struct pt_regs *regs, unsigned int address)
+{
+#ifdef CONFIG_MMU
+	/* Synchronize this task's top level page-table
+	 * with the 'reference' page table.
+	 */
+	struct mm_struct *act_mm = current->active_mm;
+	int index = pgd_index(address);
+	pgd_t *pgd, *pgd_k;
+	p4d_t *p4d, *p4d_k;
+	pud_t *pud, *pud_k;
+	pmd_t *pmd, *pmd_k;
+	pte_t *pte_k;
+
+	if (act_mm == NULL)
+		goto bad_page_fault;
+
+	pgd = act_mm->pgd + index;
+	pgd_k = init_mm.pgd + index;
+
+	if (!pgd_present(*pgd_k))
+		goto bad_page_fault;
+
+	pgd_val(*pgd) = pgd_val(*pgd_k);
+
+	p4d = p4d_offset(pgd, address);
+	p4d_k = p4d_offset(pgd_k, address);
+	if (!p4d_present(*p4d) || !p4d_present(*p4d_k))
+		goto bad_page_fault;
+
+	pud = pud_offset(p4d, address);
+	pud_k = pud_offset(p4d_k, address);
+	if (!pud_present(*pud) || !pud_present(*pud_k))
+		goto bad_page_fault;
+
+	pmd = pmd_offset(pud, address);
+	pmd_k = pmd_offset(pud_k, address);
+	if (!pmd_present(*pmd) || !pmd_present(*pmd_k))
+		goto bad_page_fault;
+
+	pmd_val(*pmd) = pmd_val(*pmd_k);
+	pte_k = pte_offset_kernel(pmd_k, address);
+
+	if (!pte_present(*pte_k))
+		goto bad_page_fault;
+	return;
+
+bad_page_fault:
+	bad_page_fault(regs, address, SIGKILL);
+#else
+	WARN_ONCE(1, "%s in noMMU configuration\n", __func__);
+#endif
+}
+/*
+ * This routine handles page faults.  It determines the address,
+ * and the problem, and then passes it off to one of the appropriate
+ * routines.
+ *
+ * Note: does not handle Miss and MultiHit.
+ */
+
+void do_page_fault(struct pt_regs *regs)
+{
+	struct vm_area_struct * vma;
+	struct mm_struct *mm = current->mm;
+	unsigned int exccause = regs->exccause;
+	unsigned int address = regs->excvaddr;
+	int code;
+
+	int is_write, is_exec;
+	vm_fault_t fault;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
+
+	code = SEGV_MAPERR;
+
+	/* We fault-in kernel-space virtual memory on-demand. The
+	 * 'reference' page table is init_mm.pgd.
+	 */
+	if (address >= TASK_SIZE && !user_mode(regs)) {
+		vmalloc_fault(regs, address);
+		return;
+	}
+
+	/* If we're in an interrupt or have no user
+	 * context, we must not take the fault..
+	 */
+	if (faulthandler_disabled() || !mm) {
+		bad_page_fault(regs, address, SIGSEGV);
+		return;
+	}
+
+	is_write = (exccause == EXCCAUSE_STORE_CACHE_ATTRIBUTE) ? 1 : 0;
+	is_exec =  (exccause == EXCCAUSE_ITLB_PRIVILEGE ||
+		    exccause == EXCCAUSE_ITLB_MISS ||
+		    exccause == EXCCAUSE_FETCH_CACHE_ATTRIBUTE) ? 1 : 0;
+
+	pr_debug("[%s:%d:%08x:%d:%08lx:%s%s]\n",
+		 current->comm, current->pid,
+		 address, exccause, regs->pc,
+		 is_write ? "w" : "", is_exec ? "x" : "");
+
+	if (user_mode(regs))
+		flags |= FAULT_FLAG_USER;
+
+	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
+
+retry:
+	vma = lock_mm_and_find_vma(mm, address, regs);
+	if (!vma)
+		goto bad_area_nosemaphore;
+
+	/* Ok, we have a good vm_area for this memory access, so
+	 * we can handle it..
+	 */
+
+	code = SEGV_ACCERR;
+
+	if (is_write) {
+		if (!(vma->vm_flags & VM_WRITE))
+			goto bad_area;
+		flags |= FAULT_FLAG_WRITE;
+	} else if (is_exec) {
+		if (!(vma->vm_flags & VM_EXEC))
+			goto bad_area;
+	} else	/* Allow read even from write-only pages. */
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
+			goto bad_area;
+
+	/* If for any reason at all we couldn't handle the fault,
+	 * make sure we exit gracefully rather than endlessly redo
+	 * the fault.
+	 */
+	fault = handle_mm_fault(vma, address, flags, regs);
+
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			bad_page_fault(regs, address, SIGKILL);
+		return;
+	}
+
+	/* The fault is fully completed (including releasing mmap lock) */
+	if (fault & VM_FAULT_COMPLETED)
+		return;
+
+	if (unlikely(fault & VM_FAULT_ERROR)) {
+		if (fault & VM_FAULT_OOM)
+			goto out_of_memory;
+		else if (fault & VM_FAULT_SIGSEGV)
+			goto bad_area;
+		else if (fault & VM_FAULT_SIGBUS)
+			goto do_sigbus;
+		BUG();
+	}
+
+	if (fault & VM_FAULT_RETRY) {
+		flags |= FAULT_FLAG_TRIED;
+
+		/* No need to mmap_read_unlock(mm) as we would
+		 * have already released it in __lock_page_or_retry
+		 * in mm/filemap.c.
+		 */
+
+		goto retry;
+	}
+
+	mmap_read_unlock(mm);
+	return;
+
+	/* Something tried to access memory that isn't in our memory map..
+	 * Fix it, but check if it's kernel or user first..
+	 */
+bad_area:
+	mmap_read_unlock(mm);
+bad_area_nosemaphore:
+	if (user_mode(regs)) {
+		force_sig_fault(SIGSEGV, code, (void *) address);
+		return;
+	}
+	bad_page_fault(regs, address, SIGSEGV);
+	return;
+
+
+	/* We ran out of memory, or some other thing happened to us that made
+	 * us unable to handle the page fault gracefully.
+	 */
+out_of_memory:
+	mmap_read_unlock(mm);
+	if (!user_mode(regs))
+		bad_page_fault(regs, address, SIGKILL);
+	else
+		pagefault_out_of_memory();
+	return;
+
+do_sigbus:
+	mmap_read_unlock(mm);
+
+	/* Send a sigbus, regardless of whether we were in kernel
+	 * or user mode.
+	 */
+	force_sig_fault(SIGBUS, BUS_ADRERR, (void *) address);
+
+	/* Kernel mode? Handle exceptions or die */
+	if (!user_mode(regs))
+		bad_page_fault(regs, address, SIGBUS);
+	return;
+}
+
+
+void
+bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
+{
+	extern void __noreturn die(const char*, struct pt_regs*, long);
+	const struct exception_table_entry *entry;
+
+	/* Are we prepared to handle this kernel fault?  */
+	if ((entry = search_exception_tables(regs->pc)) != NULL) {
+		pr_debug("%s: Exception at pc=%#010lx (%lx)\n",
+			 current->comm, regs->pc, entry->fixup);
+		regs->pc = entry->fixup;
+		return;
+	}
+
+	/* Oops. The kernel tried to access some bad page. We'll have to
+	 * terminate things with extreme prejudice.
+	 */
+	pr_alert("Unable to handle kernel paging request at virtual "
+		 "address %08lx\n pc = %08lx, ra = %08lx\n",
+		 address, regs->pc, regs->areg[0]);
+	die("Oops", regs, sig);
+}