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charset="utf-8" Legacy kernels prior to commit 4399c03c6780 ("x86/apic: Remove verify_local_APIC()") write the xAPIC ID of the boot CPU twice to verify a functioning local APIC. This results in APIC acceleration inhibited on these kernels for reason APICV_INHIBIT_REASON_APIC_ID_MODIFIED. Allow the APICV_INHIBIT_REASON_APIC_ID_MODIFIED inhibit reason to be cleared if/when the xAPIC ID is set back to the expected vcpu_id value. This occurs on the second xAPIC ID write in verify_local_APIC(). Fixes: 3743c2f02517 ("KVM: x86: inhibit APICv/AVIC on changes to APIC ID or= APIC base") Signed-off-by: Greg Edwards --- arch/x86/kvm/lapic.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index d7639d126e6c..4064d0af094d 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2075,8 +2075,13 @@ static void kvm_lapic_xapic_id_updated(struct kvm_la= pic *apic) if (KVM_BUG_ON(apic_x2apic_mode(apic), kvm)) return; =20 - if (kvm_xapic_id(apic) =3D=3D apic->vcpu->vcpu_id) + if (kvm_xapic_id(apic) =3D=3D apic->vcpu->vcpu_id) { + /* Legacy kernels prior to 4399c03c6780 write APIC ID twice. */ + if (!kvm_apicv_activated(kvm)) + kvm_clear_apicv_inhibit(kvm, + APICV_INHIBIT_REASON_APIC_ID_MODIFIED); return; + } =20 kvm_set_apicv_inhibit(apic->vcpu->kvm, APICV_INHIBIT_REASON_APIC_ID_MODIF= IED); } --=20 2.38.1