Re: [PATCH] KVM: nVMX: Expose RDPMC-exiting only when guest supports PMU

Re: [PATCH] KVM: nVMX: Expose RDPMC-exiting only when guest supports PMU

[Paolo Bonzini]

On 25/03/19 20:09, Liran Alon wrote:
> 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>
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index f6915f10e584..2634ee8c9dc8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6978,6 +6978,30 @@ 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);
> @@ -7066,6 +7090,7 @@ 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) &&
> 

Queued, thanks.

Paolo