lkml.org 
[lkml]   [2021]   [Dec]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] KVM: selftests: Avoid KVM_SET_CPUID2 after KVM_RUN in vmx_pmu_msrs_test
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 <oliver.sang@intel.com>
> Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> 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. 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;
@@ -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;
> +
> /* 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
>

\
 
 \ /
  Last update: 2021-12-15 19:01    [W:0.123 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site