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

Suravee Suthikulpanit
2019-11-14T20:16:32Z

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@amazon.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.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