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

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")
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 arch/x86/kvm/svm/svm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

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);

On Mon, Aug 25, 2025 at 06:44:28PM +0200, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> 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>
> ---
>  arch/x86/kvm/svm/svm.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

I am able to reproduce this issue with your selftest changes and I can 
confirm that this change fixes it. For this patch:
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>

- Naveen