[PATCH v5 24/33] KVM: SVM: Inhibit AVIC if vCPUs are aliased in logical mode

[Sean Christopherson]

Inhibit SVM's AVIC if multiple vCPUs are aliased to the same logical ID.
Architecturally, all CPUs whose logical ID matches the MDA are supposed
to receive the interrupt; overwriting existing entries in AVIC's
logical=>physical map can result in missed IPIs.

Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC")
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 6 ++++++
 arch/x86/kvm/lapic.c            | 5 +++++
 arch/x86/kvm/svm/avic.c         | 3 ++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5865bad08a23..b41a01b3a4af 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1218,6 +1218,12 @@ enum kvm_apicv_inhibit {
 	 * AVIC is disabled because SEV doesn't support it.
 	 */
 	APICV_INHIBIT_REASON_SEV,
+
+	/*
+	 * AVIC is disabled because not all vCPUs with a valid LDR have a 1:1
+	 * mapping between logical ID and vCPU.
+	 */
+	APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED,
 };
 
 struct kvm_arch {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 297da684c25f..0faf80cdc1be 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -396,6 +396,11 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
 	else
 		kvm_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED);
 
+	if (!new || new->logical_mode == KVM_APIC_MODE_MAP_DISABLED)
+		kvm_set_apicv_inhibit(kvm, APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED);
+	else
+		kvm_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED);
+
 	old = rcu_dereference_protected(kvm->arch.apic_map,
 			lockdep_is_held(&kvm->arch.apic_map_lock));
 	rcu_assign_pointer(kvm->arch.apic_map, new);
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index d1ac19f053ce..1fd473a57159 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -967,7 +967,8 @@ bool avic_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason)
 			  BIT(APICV_INHIBIT_REASON_SEV)      |
 			  BIT(APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED) |
 			  BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) |
-			  BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED);
+			  BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED) |
+			  BIT(APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED);
 
 	return supported & BIT(reason);
 }
-- 
2.39.0.314.g84b9a713c41-goog