Commit e51bfdb6 authored Mar 25, 2019 by Liran Alon Committed by Paolo Bonzini Apr 16, 2019

KVM: nVMX: Expose RDPMC-exiting only when guest supports PMU



Issue was discovered when running kvm-unit-tests on KVM running as L1 on
top of Hyper-V.

When vmx_instruction_intercept unit-test attempts to run RDPMC to test
RDPMC-exiting, it is intercepted by L1 KVM which it's EXIT_REASON_RDPMC
handler raise #GP because vCPU exposed by Hyper-V doesn't support PMU.
Instead of unit-test expectation to be reflected with EXIT_REASON_RDPMC.

The reason vmx_instruction_intercept unit-test attempts to run RDPMC
even though Hyper-V doesn't support PMU is because L1 expose to L2
support for RDPMC-exiting. Which is reasonable to assume that is
supported only in case CPU supports PMU to being with.

Above issue can easily be simulated by modifying
vmx_instruction_intercept config in x86/unittests.cfg to run QEMU with
"-cpu host,+vmx,-pmu" and run unit-test.

To handle issue, change KVM to expose RDPMC-exiting only when guest
supports PMU.

Reported-by: Saar Amar <saaramar@microsoft.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 672ff6cf

arch/x86/kvm/vmx/vmx.c

+25 −0

Original line number	Diff line number	Diff line
		@@ -6856,6 +6856,30 @@ static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
		}
		}

		static bool guest_cpuid_has_pmu(struct kvm_vcpu *vcpu)
		{
		struct kvm_cpuid_entry2 *entry;
		union cpuid10_eax eax;

		entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
		if (!entry)
		return false;

		eax.full = entry->eax;
		return (eax.split.version_id > 0);
		}

		static void nested_vmx_procbased_ctls_update(struct kvm_vcpu *vcpu)
		{
		struct vcpu_vmx *vmx = to_vmx(vcpu);
		bool pmu_enabled = guest_cpuid_has_pmu(vcpu);

		if (pmu_enabled)
		vmx->nested.msrs.procbased_ctls_high \|= CPU_BASED_RDPMC_EXITING;
		else
		vmx->nested.msrs.procbased_ctls_high &= ~CPU_BASED_RDPMC_EXITING;
		}

		static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
		{
		struct vcpu_vmx *vmx = to_vmx(vcpu);
		@@ -6944,6 +6968,7 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
		if (nested_vmx_allowed(vcpu)) {
		nested_vmx_cr_fixed1_bits_update(vcpu);
		nested_vmx_entry_exit_ctls_update(vcpu);
		nested_vmx_procbased_ctls_update(vcpu);
		}

		if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&

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