linux-kernel - Re: [PATCH v3 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA

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Date:   Wed, 27 Apr 2022 17:32:10 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sandipan Das <sandipan.das@....com>,
        Vasant Hegde <vasant.hegde@....com>
Cc:     peterz@...radead.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        jolsa@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        pbonzini@...hat.com, jmattson@...gle.com, eranian@...gle.com,
        puwen@...on.cn, ananth.narayan@....com, ravi.bangoria@....com,
        santosh.shukla@....com, x86@...nel.org,
        linux-perf-users@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA

On 26/4/2022 9:05 pm, Sandipan Das wrote:
> On some x86 processors, CPUID leaf 0xA provides information
> on Architectural Performance Monitoring features. It
> advertises a PMU version which Qemu uses to determine the
> availability of additional MSRs to manage the PMCs.
> 
> Upon receiving a KVM_GET_SUPPORTED_CPUID ioctl request for
> the same, the kernel constructs return values based on the
> x86_pmu_capability irrespective of the vendor.
> 
> This leaf and the additional MSRs are not supported on AMD
> and Hygon processors. If AMD PerfMonV2 is detected, the PMU

So, why not:

		if (!static_cpu_has(X86_FEATURE_ARCH_PERFMON))
			break;
?

> version is set to 2 and guest startup breaks because of an
> attempt to access a non-existent MSR. Return zeros to avoid
> this.
> 
> Fixes: a6c06ed1a60a ("KVM: Expose the architectural performance monitoring CPUID leaf")
> Reported-by: Vasant Hegde <vasant.hegde@....com>
> Signed-off-by: Sandipan Das <sandipan.das@....com>
> ---
>   arch/x86/kvm/cpuid.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 4b62d80bb22f..d27d6a8f601a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -872,6 +872,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>   		union cpuid10_eax eax;
>   		union cpuid10_edx edx;
>   
> +		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> +		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
> +			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> +			break;
> +		}
> +
>   		perf_get_x86_pmu_capability(&cap);
>   
>   		/*