FAILED: patch "[PATCH] KVM: nVMX: Service local TLB flushes on failed nested" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 05a0b701d1089fb57beeb8982f23c3bbafe0fa8b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090953-storage-unbent-4b4f@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 05a0b701d1089fb57beeb8982f23c3bbafe0fa8b Mon Sep 17 00:00:00 2001
From: Yosry Ahmed <[email protected]>
Date: Wed, 22 Jul 2026 23:01:28 +0000
Subject: [PATCH] KVM: nVMX: Service local TLB flushes on failed nested
VM-Enter

KVM services local TLB flushes on "full" nested VM-Exits (through __nested_vmx_vmexit()), but not if a nested VM-Enter fails (e.g. due to failed VMCS checks in nested_vmx_enter_non_root_mode()).

However, it is possible that KVM had queued TLB flushes that need to be performed, even if the nested VM-Enter was not successful. For example, if VPID is disabled for L2 (via nested_vmx_transition_tlb_flush(), or if via the MSR load lists, as the SDM says:

If any MSR is being loaded in such a way that would architecturally require a TLB flush, the TLBs are updated so that, after VM entry, the logical processor will not use any translations that were cached before the transition.

The SDM is unclear about when the TLB flush should occur, and whether or not a failed VM entry would flush the TLB, so it is safer to always do the TLB flush in this case.

More concretely, KVM also updates the last VPID L1 used for L2 in nested_vmx_transition_tlb_flush() (i.e. last_vpid), even if the VM entry ultimately fails. With the current code, KVM could miss a TLB flush if L1 changes L2's VPID, then does a failed VM entry followed by a successful one, as the failed VM entry would update last_vpid but not actually flush the TLB. Servicing local TLB flushes on failed VM entries makes sure that the TLB is always flushed when last_vpid is updated.

index 0635e92471c8..5d5b5022438d 100644
@@ -3765,6 +3765,14 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 vmentry_fail_vmexit_guest_mode:
 	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETTING)
 		vcpu->arch.tsc_offset -= vmcs12->tsc_offset;
+
+	/*
+	 * Handle any TLB flush requests that were queued for L2 if KVM made it
+	 * far enough along to switch to L2 context.  Note, loading host state
+	 * will generate any flushes for L1 required by VM-Exit.
+	 */
+	kvm_service_local_tlb_flush_requests(vcpu);
+
 	leave_guest_mode(vcpu);
 
 vmentry_fail_vmexit:

From: Yosry Ahmed <[email protected]>

[ Upstream commit 05a0b701d1089fb57beeb8982f23c3bbafe0fa8b ]

KVM services local TLB flushes on "full" nested VM-Exits (through __nested_vmx_vmexit()), but not if a nested VM-Enter fails (e.g. due to failed VMCS checks in nested_vmx_enter_non_root_mode()).

However, it is possible that KVM had queued TLB flushes that need to be performed, even if the nested VM-Enter was not successful. For example, if VPID is disabled for L2 (via nested_vmx_transition_tlb_flush(), or if via the MSR load lists, as the SDM says:

If any MSR is being loaded in such a way that would architecturally require a TLB flush, the TLBs are updated so that, after VM entry, the logical processor will not use any translations that were cached before the transition.

The SDM is unclear about when the TLB flush should occur, and whether or not a failed VM entry would flush the TLB, so it is safer to always do the TLB flush in this case.

More concretely, KVM also updates the last VPID L1 used for L2 in nested_vmx_transition_tlb_flush() (i.e. last_vpid), even if the VM entry ultimately fails. With the current code, KVM could miss a TLB flush if L1 changes L2's VPID, then does a failed VM entry followed by a successful one, as the failed VM entry would update last_vpid but not actually flush the TLB. Servicing local TLB flushes on failed VM entries makes sure that the TLB is always flushed when last_vpid is updated.

---
 arch/x86/kvm/vmx/nested.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index 801938b255822..90636832db684 100644
@@ -3490,6 +3490,20 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 vmentry_fail_vmexit_guest_mode:
 	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETTING)
 		vcpu->arch.tsc_offset -= vmcs12->tsc_offset;
+
+	/*
+	 * Handle any TLB flush requests that were queued for L2 if KVM made it
+	 * far enough along to switch to L2 context.  Note, loading host state
+	 * will generate any flushes for L1 required by VM-Exit.
+	 */
+	if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu))
+		kvm_vcpu_flush_tlb_current(vcpu);
+
+	if (kvm_check_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu)) {
+		++vcpu->stat.tlb_flush;
+		kvm_x86_ops.tlb_flush_guest(vcpu);
+	}
+
 	leave_guest_mode(vcpu);
 
 vmentry_fail_vmexit:

2.53.0