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

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Date:   Sat,  3 Sep 2022 00:22:48 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Li RongQing <lirongqing@...du.com>
Subject: [PATCH v2 17/23] 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")
Signed-off-by: Sean Christopherson <seanjc@...gle.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