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Message-ID: <276febe3-f61c-8c3d-b069-bbcea4217660@gmail.com>
Date: Mon, 8 Nov 2021 12:11:28 +0800
From: Like Xu <like.xu.linux@...il.com>
To: Liuxiangdong <liuxiangdong5@...wei.com>,
Zhu Lingshan <lingshan.zhu@...el.com>
Cc: seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
jmattson@...gle.com, joro@...tes.org, kan.liang@...ux.intel.com,
ak@...ux.intel.com, wei.w.wang@...el.com, eranian@...gle.com,
linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
boris.ostrvsky@...cle.com, Yao Yuan <yuan.yao@...el.com>,
Venkatesh Srinivas <venkateshs@...omium.org>,
"Fangyi (Eric)" <eric.fangyi@...wei.com>,
Xiexiangyou <xiexiangyou@...wei.com>
Subject: Re: [PATCH V10 05/18] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit
when vPMU is enabled
On 8/11/2021 12:07 pm, Liuxiangdong wrote:
>
>
> On 2021/11/8 11:06, Like Xu wrote:
>> On 7/11/2021 6:14 pm, Liuxiangdong wrote:
>>> Hi, like and lingshan.
>>>
>>> As said, IA32_MISC_ENABLE[7] bit depends on the PMU is enabled for the
>>> guest, so a software
>>> write openration to this bit will be ignored.
>>>
>>> But, in this patch, all the openration that writes msr_ia32_misc_enable in
>>> guest could make this bit become 0.
>>>
>>> Suppose:
>>> When we start vm with "enable_pmu", vcpu->arch.ia32_misc_enable_msr may be
>>> 0x80 first.
>>> And next, guest writes msr_ia32_misc_enable value 0x1.
>>> What we want could be 0x81, but unfortunately, it will be 0x1 because of
>>> "data &= ~MSR_IA32_MISC_ENABLE_EMON;"
>>> And even if guest writes msr_ia32_misc_enable value 0x81, it will be 0x1 also.
>>>
>>
>> Yes and thank you. The fix has been committed on my private tree for a long time.
>>
>>>
>>> What we want is write operation will not change this bit. So, how about this?
>>>
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -3321,6 +3321,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
>>> msr_data *msr_info)
>>> }
>>> break;
>>> case MSR_IA32_MISC_ENABLE:
>>> + data &= ~MSR_IA32_MISC_ENABLE_EMON;
>>> + data |= (vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_EMON);
>>> if (!kvm_check_has_quirk(vcpu->kvm,
>>> KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT) &&
>>> ((vcpu->arch.ia32_misc_enable_msr ^ data) &
>>> MSR_IA32_MISC_ENABLE_MWAIT)) {
>>> if (!guest_cpuid_has(vcpu, X86_FEATURE_XMM3))
>>>
>>>
>>
>> How about this for the final state considering PEBS enabling:
>>
>> case MSR_IA32_MISC_ENABLE: {
>> u64 old_val = vcpu->arch.ia32_misc_enable_msr;
>> u64 pmu_mask = MSR_IA32_MISC_ENABLE_EMON |
>> MSR_IA32_MISC_ENABLE_EMON;
>>
> u64 pmu_mask = MSR_IA32_MISC_ENABLE_EMON |
> MSR_IA32_MISC_ENABLE_EMON;
>
> Repetitive "MSR_IA32_MISC_ENABLE_EMON" ?
Oops,
u64 pmu_mask = MSR_IA32_MISC_ENABLE_EMON |
MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
I'll send the fix after sync with Lingshan.
>
>> /* RO bits */
>> if (!msr_info->host_initiated &&
>> ((old_val ^ data) & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
>> return 1;
>>
>> /*
>> * For a dummy user space, the order of setting vPMU capabilities and
>> * initialising MSR_IA32_MISC_ENABLE is not strictly guaranteed, so to
>> * avoid inconsistent functionality we keep the vPMU bits unchanged here.
>> */
> Yes. It's a little clearer with comments.
Thanks for your feedback! Enjoy the feature.
>> data &= ~pmu_mask;
>> data |= old_val & pmu_mask;
>> if (!kvm_check_has_quirk(vcpu->kvm,
>> KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT) &&
>> ((old_val ^ data) & MSR_IA32_MISC_ENABLE_MWAIT)) {
>> if (!guest_cpuid_has(vcpu, X86_FEATURE_XMM3))
>> return 1;
>> vcpu->arch.ia32_misc_enable_msr = data;
>> kvm_update_cpuid_runtime(vcpu);
>> } else {
>> vcpu->arch.ia32_misc_enable_msr = data;
>> }
>> break;
>> }
>>
>>> Or is there anything in your design intention I don't understand?
>>>
>>> Thanks!
>>>
>>> Xiangdong Liu
>>>
>>>
>>> On 2021/8/6 21:37, Zhu Lingshan wrote:
>>>> From: Like Xu <like.xu@...ux.intel.com>
>>>>
>>>> On Intel platforms, the software can use the IA32_MISC_ENABLE[7] bit to
>>>> detect whether the processor supports performance monitoring facility.
>>>>
>>>> It depends on the PMU is enabled for the guest, and a software write
>>>> operation to this available bit will be ignored. The proposal to ignore
>>>> the toggle in KVM is the way to go and that behavior matches bare metal.
>>>>
>>>> Cc: Yao Yuan <yuan.yao@...el.com>
>>>> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
>>>> Reviewed-by: Venkatesh Srinivas <venkateshs@...omium.org>
>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>>>> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>>> ---
>>>> arch/x86/kvm/vmx/pmu_intel.c | 1 +
>>>> arch/x86/kvm/x86.c | 1 +
>>>> 2 files changed, 2 insertions(+)
>>>>
>>>> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
>>>> index 9efc1a6b8693..d9dbebe03cae 100644
>>>> --- a/arch/x86/kvm/vmx/pmu_intel.c
>>>> +++ b/arch/x86/kvm/vmx/pmu_intel.c
>>>> @@ -488,6 +488,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>>>> if (!pmu->version)
>>>> return;
>>>> + vcpu->arch.ia32_misc_enable_msr |= MSR_IA32_MISC_ENABLE_EMON;
>>>> perf_get_x86_pmu_capability(&x86_pmu);
>>>> pmu->nr_arch_gp_counters = min_t(int, eax.split.num_counters,
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index efd11702465c..f6b6984e26ef 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -3321,6 +3321,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
>>>> msr_data *msr_info)
>>>> }
>>>> break;
>>>> case MSR_IA32_MISC_ENABLE:
>>>> + data &= ~MSR_IA32_MISC_ENABLE_EMON;
>>>> if (!kvm_check_has_quirk(vcpu->kvm,
>>>> KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT) &&
>>>> ((vcpu->arch.ia32_misc_enable_msr ^ data) &
>>>> MSR_IA32_MISC_ENABLE_MWAIT)) {
>>>> if (!guest_cpuid_has(vcpu, X86_FEATURE_XMM3))
>>>
>
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