[PATCH 6.18 324/333] KVM: SVM: Add a helper to look up the max physical ID for AVIC

Greg Kroah-Hartman
2026-03-17T17:28:19Z

From: Naveen N Rao <naveen@kernel.org>

[ Upstream commit f2f6e67a56dc88fea7e9b10c4e79bb01d97386b7 ]

To help with a future change, add a helper to look up the maximum
physical ID depending on the vCPU AVIC mode. No functional change
intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
Link: https://lore.kernel.org/r/0ab9bf5e20a3463a4aa3a5ea9bbbac66beedf1d1.1757009416.git.naveen@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Stable-dep-of: 87d0f901a9bd ("KVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm/avic.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)

--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -158,13 +158,31 @@ static void avic_set_x2apic_msr_intercep
svm->x2avic_msrs_intercepted = intercept;
}

+static u32 avic_get_max_physical_id(struct kvm_vcpu *vcpu)
+{
+ u32 arch_max;
+
+ if (x2avic_enabled && apic_x2apic_mode(vcpu->arch.apic))
+ arch_max = X2AVIC_MAX_PHYSICAL_ID;
+ else
+ arch_max = AVIC_MAX_PHYSICAL_ID;
+
+ /*
+ * Despite its name, KVM_CAP_MAX_VCPU_ID represents the maximum APIC ID
+ * plus one, so the max possible APIC ID is one less than that.
+ */
+ return min(vcpu->kvm->arch.max_vcpu_ids - 1, arch_max);
+}
+
static void avic_activate_vmcb(struct vcpu_svm *svm)
{
struct vmcb *vmcb = svm->vmcb01.ptr;
- struct kvm *kvm = svm->vcpu.kvm;
+ struct kvm_vcpu *vcpu = &svm->vcpu;

vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK);
+
vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK;
+ vmcb->control.avic_physical_id |= avic_get_max_physical_id(vcpu);

vmcb->control.int_ctl |= AVIC_ENABLE_MASK;

@@ -177,8 +195,7 @@ static void avic_activate_vmcb(struct vc
*/
if (x2avic_enabled && apic_x2apic_mode(svm->vcpu.arch.apic)) {
vmcb->control.int_ctl |= X2APIC_MODE_MASK;
- vmcb->control.avic_physical_id |= min(kvm->arch.max_vcpu_ids - 1,
- X2AVIC_MAX_PHYSICAL_ID);
+
/* Disabling MSR intercept for x2APIC registers */
avic_set_x2apic_msr_interception(svm, false);
} else {
@@ -188,9 +205,6 @@ static void avic_activate_vmcb(struct vc
*/
kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu);

- /* For xAVIC and hybrid-xAVIC modes */
- vmcb->control.avic_physical_id |= min(kvm->arch.max_vcpu_ids - 1,
- AVIC_MAX_PHYSICAL_ID);
/* Enabling MSR intercept for x2APIC registers */
avic_set_x2apic_msr_interception(svm, true);
}