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Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.2.1 Subject: Re: [PATCH V10 05/18] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled Content-Language: en-US To: Liuxiangdong , Zhu Lingshan Cc: seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, kan.liang@linux.intel.com, ak@linux.intel.com, wei.w.wang@intel.com, eranian@google.com, linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, boris.ostrvsky@oracle.com, Yao Yuan , Venkatesh Srinivas , "Fangyi (Eric)" , Xiexiangyou References: <20210806133802.3528-1-lingshan.zhu@intel.com> <20210806133802.3528-6-lingshan.zhu@intel.com> <6187A6F9.5030401@huawei.com> <5aa115ab-d22c-098d-0591-36c7ab15f8b6@gmail.com> <6188A28B.2020302@huawei.com> From: Like Xu Organization: Tencent In-Reply-To: <6188A28B.2020302@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>> >>>> 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 >>>> Signed-off-by: Like Xu >>>> Reviewed-by: Venkatesh Srinivas >>>> Signed-off-by: Zhu Lingshan >>>> Acked-by: Peter Zijlstra (Intel) >>>> --- >>>>   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)) >>> >