linux-kernel - [PATCH v5 12/18] svm: Deactivate AVIC when launching guest with nested SVM support

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Date:   Thu, 14 Nov 2019 14:15:14 -0600
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, joro@...tes.org,
        vkuznets@...hat.com, rkagan@...tuozzo.com, graf@...zon.com,
        jschoenh@...zon.de, karahmed@...zon.de, rimasluk@...zon.com,
        jon.grimm@....com,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH v5 12/18] svm: Deactivate AVIC when launching guest with nested SVM support

Since AVIC does not currently work w/ nested virtualization,
deactivate AVIC for the guest if setting CPUID Fn80000001_ECX[SVM]
(i.e. indicate support for SVM, which is needed for nested virtualization).
Also, introduce a new APICV_INHIBIT_REASON_NESTED bit to be used for
this reason.

Suggested-by: Alexander Graf <graf@...zon.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm.c              | 11 ++++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5d1e4a9..6c598ca 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -851,6 +851,7 @@ enum kvm_irqchip_mode {
 
 #define APICV_INHIBIT_REASON_DISABLE    0
 #define APICV_INHIBIT_REASON_HYPERV     1
+#define APICV_INHIBIT_REASON_NESTED     2
 
 struct kvm_arch {
 	unsigned long n_used_mmu_pages;
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5e80b7e..ac4901c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5963,6 +5963,14 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu)
 		return;
 
 	guest_cpuid_clear(vcpu, X86_FEATURE_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);
 }
 
 #define F(x) bit(X86_FEATURE_##x)
@@ -7244,7 +7252,8 @@ static bool svm_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
 static bool svm_check_apicv_inhibit_reasons(ulong bit)
 {
 	ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
-			  BIT(APICV_INHIBIT_REASON_HYPERV);
+			  BIT(APICV_INHIBIT_REASON_HYPERV) |
+			  BIT(APICV_INHIBIT_REASON_NESTED);
 
 	return supported & BIT(bit);
 }
-- 
1.8.3.1