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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id o4sm8476455wmq.31.2021.12.16.01.04.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Dec 2021 01:04:14 -0800 (PST) From: Vitaly Kuznetsov To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , oliver.sang@intel.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: selftests: Avoid KVM_SET_CPUID2 after KVM_RUN in vmx_pmu_msrs_test In-Reply-To: References: <20211215161617.246563-1-vkuznets@redhat.com> Date: Thu, 16 Dec 2021 10:04:13 +0100 Message-ID: <87a6h0vs36.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > On Wed, Dec 15, 2021, Vitaly Kuznetsov wrote: >> Commit feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") >> forbade chaning vCPU's CPUID data after the first KVM_RUN but >> vmx_pmu_msrs_test does exactly that. Test VM needs to be re-created after >> vcpu_run(). >> >> Reported-by: kernel test robot >> Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") >> Signed-off-by: Vitaly Kuznetsov >> --- >> tools/testing/selftests/kvm/x86_64/vmx_pmu_msrs_test.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/tools/testing/selftests/kvm/x86_64/vmx_pmu_msrs_test.c b/tools/testing/selftests/kvm/x86_64/vmx_pmu_msrs_test.c >> index 23051d84b907..17882f79deed 100644 >> --- a/tools/testing/selftests/kvm/x86_64/vmx_pmu_msrs_test.c >> +++ b/tools/testing/selftests/kvm/x86_64/vmx_pmu_msrs_test.c >> @@ -99,6 +99,11 @@ int main(int argc, char *argv[]) >> vcpu_run(vm, VCPU_ID); >> ASSERT_EQ(vcpu_get_msr(vm, VCPU_ID, MSR_IA32_PERF_CAPABILITIES), PMU_CAP_FW_WRITES); >> >> + /* Re-create guest VM after KVM_RUN so CPUID can be changed */ >> + kvm_vm_free(vm); >> + vm = vm_create_default(VCPU_ID, 0, guest_code); >> + vcpu_set_cpuid(vm, VCPU_ID, cpuid); > > Why is this test even setting CPUID for the below cases? Guest CPUID shouldn't > affect host_initiated writes. This part in particular looks wrong: > > entry_1_0->ecx |= X86_FEATURE_PDCM; > eax.split.version_id = 0; > entry_1_0->ecx = eax.full; > vcpu_set_cpuid(vm, VCPU_ID, cpuid); > ret = _vcpu_set_msr(vm, 0, MSR_IA32_PERF_CAPABILITIES, PMU_CAP_FW_WRITES); > TEST_ASSERT(ret == 0, "Bad PERF_CAPABILITIES didn't fail."); > > As does the KVM code. I admit my natural laziness and thanks for going the extra mile here! > The WRMSR path for MSR_IA32_PERF_CAPABILITIES looks especially > wrong, as rejects a bad write iff userspace set PDCM in guest CPUID. > > struct kvm_msr_entry msr_ent = {.index = msr, .data = 0}; > > if (!msr_info->host_initiated) > return 1; > if (guest_cpuid_has(vcpu, X86_FEATURE_PDCM) && kvm_get_msr_feature(&msr_ent)) <===== Huh? > return 1; > if (data & ~msr_ent.data) > return 1; > > vcpu->arch.perf_capabilities = data; > > return 0; > } > > So I think we should fix KVM and then clean up the test accordingly. > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 85127b3e3690..65e297875405 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3424,7 +3424,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > if (!msr_info->host_initiated) > return 1; > - if (guest_cpuid_has(vcpu, X86_FEATURE_PDCM) && kvm_get_msr_feature(&msr_ent)) > + if (kvm_get_msr_feature(&msr_ent)) > return 1; > if (data & ~msr_ent.data) > return 1; This looks OK. > @@ -3779,14 +3779,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > msr_info->data = vcpu->arch.microcode_version; > break; > case MSR_IA32_ARCH_CAPABILITIES: > - if (!msr_info->host_initiated && > - !guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES)) > + if (!msr_info->host_initiated) > return 1; > msr_info->data = vcpu->arch.arch_capabilities; > break; > case MSR_IA32_PERF_CAPABILITIES: > - if (!msr_info->host_initiated && > - !guest_cpuid_has(vcpu, X86_FEATURE_PDCM)) > + if (!msr_info->host_initiated) > return 1; > msr_info->data = vcpu->arch.perf_capabilities; > break; > Hm, this change will unconditionally forbid reading MSR_IA32_ARCH_CAPABILITIES/MSR_IA32_PERF_CAPABILITIES from the guest. Is this what we want? >> + >> /* testcase 2, check valid LBR formats are accepted */ >> vcpu_set_msr(vm, 0, MSR_IA32_PERF_CAPABILITIES, 0); >> ASSERT_EQ(vcpu_get_msr(vm, VCPU_ID, MSR_IA32_PERF_CAPABILITIES), 0); >> -- >> 2.33.1 >> > -- Vitaly