[PATCH v2 17/23] KVM: SVM: Inhibit AVIC if vCPUs are aliased in logical mode

Sean Christopherson
2022-09-03T00:24:26Z

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")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
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 13dadc96d9ac..042dcdf987d2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1144,6 +1144,12 @@ enum kvm_apicv_inhibit {
* inhibits, this is sticky for simplicity.
*/
APICV_INHIBIT_REASON_X2APIC,
+
+ /*
+ * 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 407e933eb073..4cebbdd3431b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -364,6 +364,11 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
cluster[ldr] = apic;
}
out:
+ 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 3400046ad0b4..efb0632d7457 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -994,7 +994,8 @@ bool avic_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason)
BIT(APICV_INHIBIT_REASON_SEV) |
BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) |
BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED) |
- BIT(APICV_INHIBIT_REASON_X2APIC);
+ BIT(APICV_INHIBIT_REASON_X2APIC) |
+ BIT(APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED);

return supported & BIT(reason);
}
--
2.37.2.789.g6183377224-goog