linux-kernel - Re: [PATCH 7/7] kvm: x86/cpuid: Fix Architectural Performance Monitoring support

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Message-ID: <7c3c082c-2cad-44ae-1b66-6b1ab73dc11e@gmail.com>
Date:   Tue, 22 Mar 2022 15:31:43 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sandipan Das <sandipan.das@....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,
        ananth.narayan@....com, ravi.bangoria@....com,
        santosh.shukla@....com, kvm list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 7/7] kvm: x86/cpuid: Fix Architectural Performance
 Monitoring support

On 17/3/2022 2:28 pm, Sandipan Das wrote:
> CPUID 0xA provides information on Architectural Performance
> Monitoring features on some x86 processors. 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 CPUID function and additional MSRs are not supported on
> AMD processors. If PerfMonV2 is detected, the PMU 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>

The new 0003 patch introduces this issue (and more kvm issues)
due to "x86_pmu.version = 2", so this is not a fix in the strictest sense.

Btw, do you need my effort to virtualize AMD PerfMonV2 ?

> Signed-off-by: Sandipan Das <sandipan.das@....com>
> ---
>   arch/x86/kvm/cpuid.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index b8f8d268d058..1d9ca5726167 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -865,6 +865,11 @@ 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) {
> +			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> +			break;
> +		}
> +
>   		perf_get_x86_pmu_capability(&cap);
>   
>   		/*