Commit cc7f5577 authored by Oliver Upton's avatar Oliver Upton Committed by Paolo Bonzini
Browse files

KVM: SVM: Inhibit APIC virtualization for X2APIC guest 



The AVIC does not support guest use of the x2APIC interface. Currently,
KVM simply chooses to squash the x2APIC feature in the guest's CPUID
If the AVIC is enabled. Doing so prevents KVM from running a guest
with greater than 255 vCPUs, as such a guest necessitates the use
of the x2APIC interface.

Instead, inhibit AVIC enablement on a per-VM basis whenever the x2APIC
feature is set in the guest's CPUID.

Signed-off-by: default avatarOliver Upton <oupton@google.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4d395762

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -886,6 +886,7 @@ enum kvm_irqchip_mode { 
#define APICV_INHIBIT_REASON_NESTED     2

#define APICV_INHIBIT_REASON_IRQWIN     3

#define APICV_INHIBIT_REASON_PIT_REINJ  4

#define APICV_INHIBIT_REASON_X2APIC	5



struct kvm_arch {

	unsigned long n_used_mmu_pages;

arch/x86/kvm/svm.c

+9 −6
Original line number Diff line number Diff line
@@ -6014,7 +6014,13 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu) 
	if (!kvm_vcpu_apicv_active(vcpu))

		return;



	guest_cpuid_clear(vcpu, X86_FEATURE_X2APIC);

	/*

	 * 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);



	/*

	 * Currently, AVIC does not work with nested virtualization.
@@ -6030,10 +6036,6 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu) 
static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)

{

	switch (func) {

	case 0x1:

		if (avic)

			entry->ecx &= ~F(X2APIC);

		break;

	case 0x80000001:

		if (nested)

			entry->ecx |= (1 << 2); /* Set SVM bit */
@@ -7357,7 +7359,8 @@ static bool svm_check_apicv_inhibit_reasons(ulong bit) 
			  BIT(APICV_INHIBIT_REASON_HYPERV) |

			  BIT(APICV_INHIBIT_REASON_NESTED) |

			  BIT(APICV_INHIBIT_REASON_IRQWIN) |

			  BIT(APICV_INHIBIT_REASON_PIT_REINJ);

			  BIT(APICV_INHIBIT_REASON_PIT_REINJ) |

			  BIT(APICV_INHIBIT_REASON_X2APIC);



	return supported & BIT(bit);

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE