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SubjectRe: [PATCH] selftests: kvm/x86: test if it checks all the bits in the LBR_FMT bit-field
From
On 5/8/2022 7:26 am, Sean Christopherson wrote:
> On Thu, Aug 04, 2022, Like Xu wrote:
>> From: Like Xu <likexu@tencent.com>
>>
>> User space only enable guest LBR feature when the exactly supported
>> LBR format value is initialized to the MSR_IA32_PERF_CAPABILITIES.
>> The input is also invalid if only partially supported bits are set.
>>
>> Note for PEBS feature, the PEBS_FORMAT bit field is the primary concern,
>> thus if the PEBS_FORMAT input is empty, the other bits check about PEBS
>> (like PEBS_TRAP or ARCH_REG) will be ignored.
>>
>> Signed-off-by: Like Xu <likexu@tencent.com>
>> ---
>> tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
>> index 6ec901dab61e..98483947f921 100644
>> --- a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
>> +++ b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
>> @@ -13,6 +13,7 @@
>>
>> #define _GNU_SOURCE /* for program_invocation_short_name */
>> #include <sys/ioctl.h>
>> +#include <linux/bitmap.h>
>>
>> #include "kvm_util.h"
>> #include "vmx.h"
>> @@ -56,7 +57,7 @@ int main(int argc, char *argv[])
>> const struct kvm_cpuid_entry2 *entry_a_0;
>> struct kvm_vm *vm;
>> struct kvm_vcpu *vcpu;
>> - int ret;
>> + int ret, bit;
>> union cpuid10_eax eax;
>> union perf_capabilities host_cap;
>>
>> @@ -97,6 +98,12 @@ int main(int argc, char *argv[])
>> ret = _vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, 0x30);
>> TEST_ASSERT(ret == 0, "Bad PERF_CAPABILITIES didn't fail.");
>>
>> + /* testcase 4, reject LBR_FMT if only partially supported bits are set */
>> + for_each_set_bit(bit, (unsigned long *)&host_cap.capabilities, 6) {
>> + ret = _vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, BIT_ULL(bit));
>> + TEST_ASSERT(ret == 0, "Bad PERF_CAPABILITIES didn't fail.");
>> + }
>
> Rather than add another testcase and target only a subset of possible values, what
> about replacing (fixing IMO) testcase #3 with fully exhaustive approach?

Yeah, much better.

>
> ---
> From: Sean Christopherson <seanjc@google.com>
> Date: Thu, 4 Aug 2022 12:18:15 -0700
> Subject: [PATCH] KVM: selftests: Test all possible "invalid"
> PERF_CAPABILITIES.LBR_FMT vals
>
> Test all possible input values to verify that KVM rejects all values
> except the exact host value. Due to the LBR format affecting the core
> functionality of LBRs, KVM can't emulate "other" formats, so even though
> there are a variety of legal values, KVM should reject anything but an
> exact host match.
>
> Suggested-by: Like Xu <like.xu.linux@gmail.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> .../selftests/kvm/x86_64/vmx_pmu_caps_test.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
> index 6ec901dab61e..069589c52f41 100644
> --- a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
> @@ -59,6 +59,7 @@ int main(int argc, char *argv[])
> int ret;
> union cpuid10_eax eax;
> union perf_capabilities host_cap;
> + uint64_t val;
>
> host_cap.capabilities = kvm_get_feature_msr(MSR_IA32_PERF_CAPABILITIES);
> host_cap.capabilities &= (PMU_CAP_FW_WRITES | PMU_CAP_LBR_FMT);
> @@ -91,11 +92,17 @@ int main(int argc, char *argv[])
> vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, host_cap.lbr_format);
> ASSERT_EQ(vcpu_get_msr(vcpu, MSR_IA32_PERF_CAPABILITIES), (u64)host_cap.lbr_format);
>
> - /* testcase 3, check invalid LBR format is rejected */
> - /* Note, on Arch LBR capable platforms, LBR_FMT in perf capability msr is 0x3f,
> - * to avoid the failure, use a true invalid format 0x30 for the test. */
> - ret = _vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, 0x30);
> - TEST_ASSERT(ret == 0, "Bad PERF_CAPABILITIES didn't fail.");
> + /*
> + * Testcase 3, check that an "invalid" LBR format is rejected. Only an
> + * exact match of the host's format (and 0/disabled) is allowed.
> + */
> + for (val = 1; val <= PMU_CAP_LBR_FMT; val++) {
> + if (val == (host_cap.capabilities & PMU_CAP_LBR_FMT))

Emm,

if (val == host_cap.lbr_format)

to save a minor cost of logical operation.

> + continue;
> +
> + ret = _vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, val);
> + TEST_ASSERT(!ret, "Bad LBR FMT = 0x%lx didn't fail", val);
> + }
>
> printf("Completed perf capability tests.\n");
> kvm_vm_free(vm);
>
> base-commit: 93472b79715378a2386598d6632c654a2223267b
> --
>

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