linux-kernel - [RFCv2 PATCH 12/12] KVM: SVM: Do not inhibit APICv when x2APIC is present

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Message-ID: <20220308163926.563994-13-suravee.suthikulpanit@amd.com>
Date:   Tue, 8 Mar 2022 10:39:26 -0600
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC:     <pbonzini@...hat.com>, <mlevitsk@...hat.com>, <seanjc@...gle.com>,
        <joro@...tes.org>, <jon.grimm@....com>, <wei.huang2@....com>,
        <terry.bowman@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [RFCv2 PATCH 12/12] KVM: SVM: Do not inhibit APICv when x2APIC is present

Currently, AVIC is inhibited when booting a VM w/ x2APIC support.
This is because AVIC cannot virtualize x2APIC mode in the VM.
With x2AVIC support, the APICV_INHIBIT_REASON_X2APIC is
no longer enforced.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kvm/svm/avic.c | 21 +++++++++++++++++++++
 arch/x86/kvm/svm/svm.c  | 18 ++----------------
 arch/x86/kvm/svm/svm.h  |  1 +
 3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 015888aad8fc..e4bf4f68f332 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -21,6 +21,7 @@
 
 #include <asm/irq_remapping.h>
 
+#include "cpuid.h"
 #include "trace.h"
 #include "lapic.h"
 #include "x86.h"
@@ -159,6 +160,26 @@ void avic_vm_destroy(struct kvm *kvm)
 	spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
 }
 
+void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested)
+{
+	/*
+	 * If the X2APIC feature is exposed to the guest,
+	 * disable AVIC unless X2AVIC mode is enabled.
+	 */
+	if (avic_mode == AVIC_MODE_X1 &&
+	    guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
+		kvm_request_apicv_update(vcpu->kvm, false,
+					 APICV_INHIBIT_REASON_X2APIC);
+
+	/*
+	 * Currently, AVIC does not work with nested virtualization.
+	 * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
+	 */
+	if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
+		kvm_request_apicv_update(vcpu->kvm, false,
+					 APICV_INHIBIT_REASON_NESTED);
+}
+
 int avic_vm_init(struct kvm *kvm)
 {
 	unsigned long flags;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ce3c68a785cf..01384ccdb56c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3988,23 +3988,9 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			vcpu->arch.reserved_gpa_bits &= ~(1UL << (best->ebx & 0x3f));
 	}
 
-	if (kvm_vcpu_apicv_active(vcpu)) {
-		/*
-		 * AVIC does not work with an x2APIC mode guest. If the X2APIC feature
-		 * is exposed to the guest, disable AVIC.
-		 */
-		if (guest_cpuid_has(vcpu, X86_FEATURE_X2APIC))
-			kvm_request_apicv_update(vcpu->kvm, false,
-						 APICV_INHIBIT_REASON_X2APIC);
+	if (kvm_vcpu_apicv_active(vcpu))
+		avic_vcpu_after_set_cpuid(vcpu, nested);
 
-		/*
-		 * Currently, AVIC does not work with nested virtualization.
-		 * So, we disable AVIC when cpuid for SVM is set in the L1 guest.
-		 */
-		if (nested && guest_cpuid_has(vcpu, X86_FEATURE_SVM))
-			kvm_request_apicv_update(vcpu->kvm, false,
-						 APICV_INHIBIT_REASON_NESTED);
-	}
 	init_vmcb_after_set_cpuid(vcpu);
 }
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 19ad40b8383b..30fd9c8da9f2 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -576,6 +576,7 @@ int avic_init_vcpu(struct vcpu_svm *svm);
 void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
 void avic_vcpu_put(struct kvm_vcpu *vcpu);
 void avic_post_state_restore(struct kvm_vcpu *vcpu);
+void avic_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu, int nested);
 void svm_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
 void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu);
 bool svm_check_apicv_inhibit_reasons(ulong bit);
-- 
2.25.1