linux-kernel - [PATCH v4 11/17] svm: Deactivate AVIC when launching guest with nested SVM support

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Date:   Fri, 1 Nov 2019 22:41:35 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "rkagan@...tuozzo.com" <rkagan@...tuozzo.com>,
        "graf@...zon.com" <graf@...zon.com>,
        "jschoenh@...zon.de" <jschoenh@...zon.de>,
        "karahmed@...zon.de" <karahmed@...zon.de>,
        "rimasluk@...zon.com" <rimasluk@...zon.com>,
        "Grimm, Jon" <Jon.Grimm@....com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Subject: [PATCH v4 11/17] 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).

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              | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a6475fd..55d6476 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -856,6 +856,7 @@ enum kvm_irqchip_mode {
 
 #define APICV_DEACT_BIT_DISABLE    0
 #define APICV_DEACT_BIT_HYPERV     1
+#define APICV_DEACT_BIT_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 5b90458..7f59b1a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5984,6 +5984,14 @@ 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_DEACT_BIT_NESTED);
 }
 
 static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
-- 
1.8.3.1