Currently, kvm_lapic_xapic_id_updated() checks if the xAPIC ID in the APIC_ID register differs from the vcpu ID. If so it inhibits APICv/AVIC. However, for vcpu 256 and above, the 8-bit xAPIC ID field in the APIC_ID register cannot support 32-bit x2APIC ID causing the kvm_xapic_id() to return invalid ID and fail the comparison with the vcpu ID. This causes APICv/AVIC inhibition for VM with more than 256 vcpus due to APIVC_INHIBIT_REASON_APIC_ID_MODIFIED. In this case, when guest switch to x2APIC mode, KVM needs to clear APIVC_INHIBIT_REASON_APIC_ID_MODIFIED. Fixes: 3743c2f02517 ("KVM: x86: inhibit APICv/AVIC on changes to APIC ID or APIC base") Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> --- arch/x86/kvm/lapic.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 9dda989a1cf0..750d385b770e 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -374,6 +374,7 @@ static inline void kvm_apic_set_x2apic_id(struct kvm_lapic *apic, u32 id) kvm_lapic_set_reg(apic, APIC_ID, id); kvm_lapic_set_reg(apic, APIC_LDR, ldr); atomic_set_release(&apic->vcpu->kvm->arch.apic_map_dirty, DIRTY); + kvm_clear_apicv_inhibit(apic->vcpu->kvm, APICV_INHIBIT_REASON_APIC_ID_MODIFIED); } static inline int apic_lvt_enabled(struct kvm_lapic *apic, int lvt_type) -- 2.34.1