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

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Message-ID: <246a7466-dc61-0186-2ff2-77fe37e73c06@amd.com>
Date:   Tue, 10 May 2022 10:29:34 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-tip-commits@...r.kernel.org,
        Vasant Hegde <vasant.hegde@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        pbonzini@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [tip: perf/core] kvm: x86/cpuid: Fix CPUID leaf 0xA

Hi Boris,

On 5/9/2022 10:54 PM, Borislav Petkov wrote:
> 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?
> 

Please remove this patch and keep commit 5a1bde46f98b instead.

- Sandipan