FAILED: patch "[PATCH] KVM: SVM: Sync TPR from LAPIC into VMCB::V_TPR even if AVIC" failed to apply to 5.4-stable tree

FAILED: patch "[PATCH] KVM: SVM: Sync TPR from LAPIC into VMCB::V_TPR even if AVIC" failed to apply to 5.4-stable tree

[gregkh]

The patch below does not apply to the 5.4-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 <stable@vger.kernel.org>.

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-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x d02e48830e3fce9701265f6c5a58d9bdaf906a76
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025092122-popper-small-d970@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From d02e48830e3fce9701265f6c5a58d9bdaf906a76 Mon Sep 17 00:00:00 2001
From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
Date: Mon, 25 Aug 2025 18:44:28 +0200
Subject: [PATCH] KVM: SVM: Sync TPR from LAPIC into VMCB::V_TPR even if AVIC
 is active

Commit 3bbf3565f48c ("svm: Do not intercept CR8 when enable AVIC")
inhibited pre-VMRUN sync of TPR from LAPIC into VMCB::V_TPR in
sync_lapic_to_cr8() when AVIC is active.

AVIC does automatically sync between these two fields, however it does
so only on explicit guest writes to one of these fields, not on a bare
VMRUN.

This meant that when AVIC is enabled host changes to TPR in the LAPIC
state might not get automatically copied into the V_TPR field of VMCB.

This is especially true when it is the userspace setting LAPIC state via
KVM_SET_LAPIC ioctl() since userspace does not have access to the guest
VMCB.

Practice shows that it is the V_TPR that is actually used by the AVIC to
decide whether to issue pending interrupts to the CPU (not TPR in TASKPRI),
so any leftover value in V_TPR will cause serious interrupt delivery issues
in the guest when AVIC is enabled.

Fix this issue by doing pre-VMRUN TPR sync from LAPIC into VMCB::V_TPR
even when AVIC is enabled.

Fixes: 3bbf3565f48c ("svm: Do not intercept CR8 when enable AVIC")
Cc: stable@vger.kernel.org
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>
Link: https://lore.kernel.org/r/c231be64280b1461e854e1ce3595d70cde3a2e9d.1756139678.git.maciej.szmigiero@oracle.com
[sean: tag for stable@]
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d9931c6c4bc6..1bfebe40854f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4046,8 +4046,7 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
 	struct vcpu_svm *svm = to_svm(vcpu);
 	u64 cr8;
 
-	if (nested_svm_virtualize_tpr(vcpu) ||
-	    kvm_vcpu_apicv_active(vcpu))
+	if (nested_svm_virtualize_tpr(vcpu))
 		return;
 
 	cr8 = kvm_get_cr8(vcpu);

[PATCH 5.4.y] KVM: SVM: Sync TPR from LAPIC into VMCB::V_TPR even if AVIC is active

[Sasha Levin]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

[ Upstream commit d02e48830e3fce9701265f6c5a58d9bdaf906a76 ]

Commit 3bbf3565f48c ("svm: Do not intercept CR8 when enable AVIC")
inhibited pre-VMRUN sync of TPR from LAPIC into VMCB::V_TPR in
sync_lapic_to_cr8() when AVIC is active.

AVIC does automatically sync between these two fields, however it does
so only on explicit guest writes to one of these fields, not on a bare
VMRUN.

This meant that when AVIC is enabled host changes to TPR in the LAPIC
state might not get automatically copied into the V_TPR field of VMCB.

This is especially true when it is the userspace setting LAPIC state via
KVM_SET_LAPIC ioctl() since userspace does not have access to the guest
VMCB.

Practice shows that it is the V_TPR that is actually used by the AVIC to
decide whether to issue pending interrupts to the CPU (not TPR in TASKPRI),
so any leftover value in V_TPR will cause serious interrupt delivery issues
in the guest when AVIC is enabled.

Fix this issue by doing pre-VMRUN TPR sync from LAPIC into VMCB::V_TPR
even when AVIC is enabled.

Fixes: 3bbf3565f48c ("svm: Do not intercept CR8 when enable AVIC")
Cc: stable@vger.kernel.org
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>
Link: https://lore.kernel.org/r/c231be64280b1461e854e1ce3595d70cde3a2e9d.1756139678.git.maciej.szmigiero@oracle.com
[sean: tag for stable@]
Signed-off-by: Sean Christopherson <seanjc@google.com>
[ Adjust context ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index e9444e202c334..cb3c86014adbd 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5580,8 +5580,7 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
 	struct vcpu_svm *svm = to_svm(vcpu);
 	u64 cr8;
 
-	if (svm_nested_virtualize_tpr(vcpu) ||
-	    kvm_vcpu_apicv_active(vcpu))
+	if (svm_nested_virtualize_tpr(vcpu))
 		return;
 
 	cr8 = kvm_get_cr8(vcpu);
-- 
2.51.0