FAILED: patch "[PATCH] KVM: x86/mmu: Drop/zap existing present SPTE even when" failed to apply to 6.1-stable tree

PATCH New [email protected] 2 participants 2 messages Mar 30 – Mar 31

Subsystems (3)

Stable branch x86 KVM x86

lore

Share & tools

lore

[email protected]

author maintainer

2026-03-30 09:45 UTC #0 lore raw

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x aad885e774966e97b675dfe928da164214a71605
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026033049-dial-everyone-46da@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From aad885e774966e97b675dfe928da164214a71605 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Thu, 5 Mar 2026 17:28:04 -0800
Subject: [PATCH] KVM: x86/mmu: Drop/zap existing present SPTE even when
creating an MMIO SPTE

When installing an emulated MMIO SPTE, do so *after* dropping/zapping the existing SPTE (if it's shadow-present). While commit a54aa15c6bda3 was right about it being impossible to convert a shadow-present SPTE to an MMIO SPTE due to a _guest_ write, it failed to account for writes to guest memory that are outside the scope of KVM.

E.g. if host userspace modifies a shadowed gPTE to switch from a memslot to emulted MMIO and then the guest hits a relevant page fault, KVM will install the MMIO SPTE without first zapping the shadow-present SPTE.

  ------------[ cut here ]------------
  is_shadow_present_pte(*sptep)
  WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292
  Modules linked in: kvm_intel kvm irqbypass
  CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm]
  Call Trace:
   <TASK>
   mmu_set_spte+0x237/0x440 [kvm]
   ept_page_fault+0x535/0x7f0 [kvm]
   kvm_mmu_do_page_fault+0xee/0x1f0 [kvm]
   kvm_mmu_page_fault+0x8d/0x620 [kvm]
   vmx_handle_exit+0x18c/0x5a0 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm]
   kvm_vcpu_ioctl+0x2d5/0x980 [kvm]
   __x64_sys_ioctl+0x8a/0xd0
   do_syscall_64+0xb5/0x730
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
  RIP: 0033:0x47fa3f
   </TASK>
  ---[ end trace 0000000000000000 ]---

Reported-by Alexander Bulekov <[email protected]>

Debugged-by Alexander Bulekov <[email protected]>

Fixes a54aa15c6bda3 ("KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte()")

Cc [email protected]

Signed-off-by Sean Christopherson <[email protected]>

arch/x86/kvm/mmu/mmu.c +8 -6

index b922a8b00057..98406d6aa2d6 100644
@@ -3044,12 +3044,6 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 	bool prefetch = !fault || fault->prefetch;
 	bool write_fault = fault && fault->write;
 
-	if (unlikely(is_noslot_pfn(pfn))) {
-		vcpu->stat.pf_mmio_spte_created++;
-		mark_mmio_spte(vcpu, sptep, gfn, pte_access);
-		return RET_PF_EMULATE;
-	}
-
 	if (is_shadow_present_pte(*sptep)) {
 		if (prefetch && is_last_spte(*sptep, level) &&
 		    pfn == spte_to_pfn(*sptep))

@@ -3073,6 +3067,14 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 			was_rmapped = 1;
 	}
 
+	if (unlikely(is_noslot_pfn(pfn))) {
+		vcpu->stat.pf_mmio_spte_created++;
+		mark_mmio_spte(vcpu, sptep, gfn, pte_access);
+		if (flush)
+			kvm_flush_remote_tlbs_gfn(vcpu->kvm, gfn, level);
+		return RET_PF_EMULATE;
+	}
+
 	wrprot = make_spte(vcpu, sp, slot, pte_access, gfn, pfn, *sptep, prefetch,
 			   false, host_writable, &spte);

Sasha Levin

maintainer

2026-03-31 23:17 UTC #1 lore raw

PATCH 1/1 KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

From: Sean Christopherson <[email protected]>

[ Upstream commit aad885e774966e97b675dfe928da164214a71605 ]

  ------------[ cut here ]------------
  is_shadow_present_pte(*sptep)
  WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292
  Modules linked in: kvm_intel kvm irqbypass
  CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm]
  Call Trace:
   <TASK>
   mmu_set_spte+0x237/0x440 [kvm]
   ept_page_fault+0x535/0x7f0 [kvm]
   kvm_mmu_do_page_fault+0xee/0x1f0 [kvm]
   kvm_mmu_page_fault+0x8d/0x620 [kvm]
   vmx_handle_exit+0x18c/0x5a0 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm]
   kvm_vcpu_ioctl+0x2d5/0x980 [kvm]
   __x64_sys_ioctl+0x8a/0xd0
   do_syscall_64+0xb5/0x730
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
  RIP: 0033:0x47fa3f
   </TASK>
  ---[ end trace 0000000000000000 ]---

Reported-by Alexander Bulekov <[email protected]>

Debugged-by Alexander Bulekov <[email protected]>

Fixes a54aa15c6bda3 ("KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte()")

Cc [email protected]

Signed-off-by Sean Christopherson <[email protected]>

[ replaced kvm_flush_remote_tlbs_gfn() with kvm_flush_remote_tlbs_with_address() and preserved pgprintk call ]

Signed-off-by Sasha Levin <[email protected]>

---
 arch/x86/kvm/mmu/mmu.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

arch/x86/kvm/mmu/mmu.c +9 -6

index 04d060f370535..ed5ba38bec869 100644
@@ -2814,12 +2814,6 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 	pgprintk("%s: spte %llx write_fault %d gfn %llx\n", __func__,
 		 *sptep, write_fault, gfn);
 
-	if (unlikely(is_noslot_pfn(pfn))) {
-		vcpu->stat.pf_mmio_spte_created++;
-		mark_mmio_spte(vcpu, sptep, gfn, pte_access);
-		return RET_PF_EMULATE;
-	}
-
 	if (is_shadow_present_pte(*sptep)) {
 		/*
 		 * If we overwrite a PTE page pointer with a 2MB PMD, unlink

@@ -2841,6 +2835,15 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 			was_rmapped = 1;
 	}
 
+	if (unlikely(is_noslot_pfn(pfn))) {
+		vcpu->stat.pf_mmio_spte_created++;
+		mark_mmio_spte(vcpu, sptep, gfn, pte_access);
+		if (flush)
+			kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn,
+					KVM_PAGES_PER_HPAGE(level));
+		return RET_PF_EMULATE;
+	}
+
 	wrprot = make_spte(vcpu, sp, slot, pte_access, gfn, pfn, *sptep, prefetch,
 			   true, host_writable, &spte);

Signature · 1 line

2.53.0