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Date: Sat, 13 Jun 2020 17:42:50 +0800
From: "Xu, Like" <like.xu@...el.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>,
Like Xu <like.xu@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, ak@...ux.intel.com,
wei.w.wang@...el.com, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org
Subject: Re: [PATCH v12 07/11] KVM: vmx/pmu: Unmask LBR fields in the
MSR_IA32_DEBUGCTLMSR emualtion
On 2020/6/13 17:14, Xiaoyao Li wrote:
> On 6/13/2020 4:09 PM, Like Xu wrote:
>> When the LBR feature is reported by the vmx_get_perf_capabilities(),
>> the LBR fields in the [vmx|vcpu]_supported debugctl should be unmasked.
>>
>> The debugctl msr is handled separately in vmx/svm and they're not
>> completely identical, hence remove the common msr handling code.
>>
>> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
>> ---
>> arch/x86/kvm/vmx/capabilities.h | 12 ++++++++++++
>> arch/x86/kvm/vmx/pmu_intel.c | 19 +++++++++++++++++++
>> arch/x86/kvm/x86.c | 13 -------------
>> 3 files changed, 31 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx/capabilities.h
>> b/arch/x86/kvm/vmx/capabilities.h
>> index b633a90320ee..f6fcfabb1026 100644
>> --- a/arch/x86/kvm/vmx/capabilities.h
>> +++ b/arch/x86/kvm/vmx/capabilities.h
>> @@ -21,6 +21,8 @@ extern int __read_mostly pt_mode;
>> #define PMU_CAP_FW_WRITES (1ULL << 13)
>> #define PMU_CAP_LBR_FMT 0x3f
>> +#define DEBUGCTLMSR_LBR_MASK (DEBUGCTLMSR_LBR |
>> DEBUGCTLMSR_FREEZE_LBRS_ON_PMI)
>> +
>> struct nested_vmx_msrs {
>> /*
>> * We only store the "true" versions of the VMX capability MSRs. We
>> @@ -387,4 +389,14 @@ static inline u64 vmx_get_perf_capabilities(void)
>> return perf_cap;
>> }
>> +static inline u64 vmx_get_supported_debugctl(void)
>> +{
>> + u64 val = 0;
>> +
>> + if (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT)
>> + val |= DEBUGCTLMSR_LBR_MASK;
>> +
>> + return val;
>> +}
>> +
>> #endif /* __KVM_X86_VMX_CAPS_H */
>> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
>> index a953c7d633f6..d92e95b64c74 100644
>> --- a/arch/x86/kvm/vmx/pmu_intel.c
>> +++ b/arch/x86/kvm/vmx/pmu_intel.c
>> @@ -187,6 +187,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu
>> *vcpu, u32 msr)
>> case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
>> ret = pmu->version > 1;
>> break;
>> + case MSR_IA32_DEBUGCTLMSR:
>> case MSR_IA32_PERF_CAPABILITIES:
>> ret = 1;
>> break;
>> @@ -237,6 +238,9 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu,
>> struct msr_data *msr_info)
>> return 1;
>> msr_info->data = vcpu->arch.perf_capabilities;
>> return 0;
>> + case MSR_IA32_DEBUGCTLMSR:
>> + msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
>
> Can we put the emulation of MSR_IA32_DEBUGCTLMSR in vmx_{get/set})_msr().
> AFAIK, MSR_IA32_DEBUGCTLMSR is not a pure PMU related MSR that there is
> bit 2 to enable #DB for bus lock.
We already have "case MSR_IA32_DEBUGCTLMSR" handler in the vmx_set_msr()
and you may apply you bus lock changes in that handler.
>> + return 0;
>> default:
>> if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>> (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
>> @@ -282,6 +286,16 @@ static inline bool lbr_is_compatible(struct
>> kvm_vcpu *vcpu)
>> return true;
>> }
>> +static inline u64 vcpu_get_supported_debugctl(struct kvm_vcpu *vcpu)
>> +{
>> + u64 debugctlmsr = vmx_get_supported_debugctl();
>> +
>> + if (!lbr_is_enabled(vcpu))
>> + debugctlmsr &= ~DEBUGCTLMSR_LBR_MASK;
>> +
>> + return debugctlmsr;
>> +}
>> +
>> static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data
>> *msr_info)
>> {
>> struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>> @@ -336,6 +350,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu,
>> struct msr_data *msr_info)
>> }
>> vcpu->arch.perf_capabilities = data;
>> return 0;
>> + case MSR_IA32_DEBUGCTLMSR:
>> + if (data & ~vcpu_get_supported_debugctl(vcpu))
>> + return 1;
>> + vmcs_write64(GUEST_IA32_DEBUGCTL, data);
>> + return 0;
>> default:
>> if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>> (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 00c88c2f34e4..56f275eb4554 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2840,18 +2840,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu,
>> struct msr_data *msr_info)
>> return 1;
>> }
>> break;
>> - case MSR_IA32_DEBUGCTLMSR:
>> - if (!data) {
>> - /* We support the non-activated case already */
>> - break;
>> - } else if (data & ~(DEBUGCTLMSR_LBR | DEBUGCTLMSR_BTF)) {
>
> So after this patch, guest trying to set bit DEBUGCTLMSR_BTF will get a
> #GP instead of being ignored and printing a log in kernel.
>
Since the BTF is not implemented on the KVM at all,
I do propose not left this kind of dummy thing in the future KVM code.
Let's see if Netware or any BTF user will complain about this change.
> These codes were introduced ~12 years ago in commit b5e2fec0ebc3 ("KVM:
> Ignore DEBUGCTL MSRs with no effect"), just to make Netware happy. Maybe
> I'm overthinking for that too old thing.
>
>> - /* Values other than LBR and BTF are vendor-specific,
>> - thus reserved and should throw a #GP */
>> - return 1;
>> - }
>> - vcpu_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTLMSR 0x%llx, nop\n",
>> - __func__, data);
>> - break;
>> case 0x200 ... 0x2ff:
>> return kvm_mtrr_set_msr(vcpu, msr, data);
>> case MSR_IA32_APICBASE:
>> @@ -3120,7 +3108,6 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu,
>> struct msr_data *msr_info)
>> switch (msr_info->index) {
>> case MSR_IA32_PLATFORM_ID:
>> case MSR_IA32_EBL_CR_POWERON:
>> - case MSR_IA32_DEBUGCTLMSR:
>> case MSR_IA32_LASTBRANCHFROMIP:
>> case MSR_IA32_LASTBRANCHTOIP:
>> case MSR_IA32_LASTINTFROMIP:
>>
>
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