KVM: SVM: Inhibit AVIC if vCPUs are aliased in logical mode

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@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230106011306.85230-25-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5865bad..b41a01b 100644 (file)
--- 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 297da68..0faf80c 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -396,6 +396,11 @@ out:
        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 d1ac19f..1fd473a 100644 (file)
--- 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);
 }