Re: [PATCH v3 05/11] KVM: selftests: Test consistency of CPUID with num of gp counters

[Sean Christopherson]

On Mon, Aug 14, 2023, Jinrong Liang wrote:
> From: Jinrong Liang <cloudliang@xxxxxxxxxxx>
> 
> Add test to check if non-existent counters can be accessed in guest after
> determining the number of Intel generic performance counters by CPUID.
> When the num of counters is less than 3, KVM does not emulate #GP if
> a counter isn't present due to compatibility MSR_P6_PERFCTRx handling.
> Nor will the KVM emulate more counters than it can support.
> 
> Co-developed-by: Like Xu <likexu@xxxxxxxxxxx>
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> Signed-off-by: Jinrong Liang <cloudliang@xxxxxxxxxxx>
> ---
>  .../kvm/x86_64/pmu_basic_functionality_test.c | 78 +++++++++++++++++++
>  1 file changed, 78 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> index daa45aa285bb..b86033e51d5c 100644
> --- a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> @@ -16,6 +16,11 @@
>  /* Guest payload for any performance counter counting */
>  #define NUM_BRANCHES			10
>  
> +static const uint64_t perf_caps[] = {
> +	0,
> +	PMU_CAP_FW_WRITES,
> +};
> +
>  static struct kvm_vm *pmu_vm_create_with_one_vcpu(struct kvm_vcpu **vcpu,
>  						  void *guest_code)
>  {
> @@ -164,6 +169,78 @@ static void intel_test_arch_events(void)
>  	}
>  }
>  
> +static void guest_wr_and_rd_msrs(uint32_t base, uint8_t begin, uint8_t offset)
> +{
> +	uint8_t wr_vector, rd_vector;
> +	uint64_t msr_val;
> +	unsigned int i;
> +
> +	for (i = begin; i < begin + offset; i++) {
> +		wr_vector = wrmsr_safe(base + i, 0xffff);
> +		rd_vector = rdmsr_safe(base + i, &msr_val);
> +		if (wr_vector == GP_VECTOR || rd_vector == GP_VECTOR)
> +			GUEST_SYNC(GP_VECTOR);

Rather than pass around the "expected" vector, and shuffle #GP vs. the msr_val
up (which can get false negatives if msr_val == 13), just read
MSR_IA32_PERF_CAPABILITIES from within the guest and GUEST_ASSERT accordingly.