linux-kernel - Re: [PATCH v2 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA

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Message-ID: <25e89d27-d7da-2dea-dd20-0a9d8dcdee83@hygon.cn>
Date:   Tue, 26 Apr 2022 11:45:32 +0000
From:   Wen Pu <puwen@...on.cn>
To:     Sandipan Das <sandipan.das@....com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "acme@...nel.org" <acme@...nel.org>,
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        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
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        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "ravi.bangoria@....com" <ravi.bangoria@....com>,
        "santosh.shukla@....com" <santosh.shukla@....com>
Subject: Re: [PATCH v2 7/7] kvm: x86/cpuid: Fix CPUID leaf 0xA

On 2022/4/26 16:40, Sandipan Das wrote:
> Hi Peter,
> 
> On 4/26/2022 1:45 PM, Peter Zijlstra wrote:
>> On Thu, Apr 21, 2022 at 11:16:59AM +0530, 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
>>> 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>
>>> ---
>>>   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 4b62d80bb22f..6bd65cad75ef 100644
>>> --- a/arch/x86/kvm/cpuid.c
>>> +++ b/arch/x86/kvm/cpuid.c
>>> @@ -872,6 +872,11 @@ 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) {
>>
>> This is the obligatory question about HYGON; should they be included
>> here?
>>
>> x86 is getting a number of me-too patches from both sides, where
>> behaviour has diverged for no raisin and then needs to be fixed up
>> again.
>>
> 
>  From what I understand, Hygon processors also do not support this leaf.
> Copying Pu Wen for confirmation.

Hi Peter, Sandipan：

I have confirmed that Hygon processors do not support CPUID leaf 0xA.
Sandipan, could you please also add X86_VENDOR_HYGON in the if
conditional?

-- 
Regards,
Pu Wen

> - Sandipan
> 
>>> +			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
>>> +			break;
>>> +		}
>>> +
>>>   		perf_get_x86_pmu_capability(&cap);
>>>   
>>>   		/*
>>> -- 
>>> 2.32.0
>>>