linux-kernel - Re: [tip: perf/core] kvm: x86/cpuid: Fix CPUID leaf 0xA

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Date:   Mon, 9 May 2022 19:24:00 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sandipan Das <sandipan.das@....com>
Cc:     linux-tip-commits@...r.kernel.org,
        Vasant Hegde <vasant.hegde@....com>,
        Sandipan Das <sandipan.das@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [tip: perf/core] kvm: x86/cpuid: Fix CPUID leaf 0xA

On Fri, Apr 29, 2022 at 08:28:48PM -0000, tip-bot2 for Sandipan Das wrote:
> The following commit has been merged into the perf/core branch of tip:
> 
> Commit-ID:     fafd15ab6dc1fdfff66908e6d9231b124e1875cf
> Gitweb:        https://git.kernel.org/tip/fafd15ab6dc1fdfff66908e6d9231b124e1875cf
> Author:        Sandipan Das <sandipan.das@....com>
> AuthorDate:    Thu, 21 Apr 2022 11:16:59 +05:30
> Committer:     Peter Zijlstra <peterz@...radead.org>
> CommitterDate: Fri, 29 Apr 2022 11:06:27 +02:00
> 
> kvm: x86/cpuid: Fix CPUID leaf 0xA
> 
> 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
> 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>
> Signed-off-by: Sandipan Das <sandipan.das@....com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/54bc7fe4cadf6bdef823bab1fba43d4891d2e1a9.1650515382.git.sandipan.das@amd.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 b24ca7f..ae1d963 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -887,6 +887,12 @@ 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;
> +		}
> +

This is all fine and dandy but this patch in tip conflicts with the very
similar patch of yours:

  5a1bde46f98b ("kvm: x86/cpuid: Only provide CPUID leaf 0xA if host has architectural PMU")

which is already upstream.

So which is it? Should we zap this version in tip instead?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette