On Wed, Jun 15, 2022, Yang Weijiang wrote:
> Read MSR_IA32_PERF_CAPABILITIES triggers #GP when pmu is disabled
> by enable_pmu=0 in KVM. Let's check whether pmu is available before
> issue msr reading to avoid the #GP. Also check PDCM bit before read
> the MSR.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
> x86/pmu_lbr.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
> index 688634d..62614a0 100644
> --- a/x86/pmu_lbr.c
> +++ b/x86/pmu_lbr.c
> @@ -5,6 +5,7 @@
> #define N 1000000
> #define MAX_NUM_LBR_ENTRY 32
> #define DEBUGCTLMSR_LBR (1UL << 0)
> +#define PDCM_ENABLED (1UL << 15)
> #define PMU_CAP_LBR_FMT 0x3f
>
> #define MSR_LBR_NHM_FROM 0x00000680
> @@ -74,13 +75,22 @@ int main(int ac, char **av)
> return 0;
> }
>
> - perf_cap = rdmsr(MSR_IA32_PERF_CAPABILITIES);
> eax.full = id.a;
>
> if (!eax.split.version_id) {
> printf("No pmu is detected!\n");
> return report_summary();
> }
> +
> + id = cpuid(1);
> +
> + if (!(id.c & PDCM_ENABLED)) {
Don't open code cpuid(), add and use X86_FEATURE_PDCM:
#define X86_FEATURE_PDCM (CPUID(0x1, 0, ECX, 15))
if (!this_cpu_has(X86_FEATURE_PDCM))
...
> + printf("No PDCM is detected!\n");
If your going to bother printing a message, please make it useful. Every time I
read PMU code I have to reread the kernel's cpufeatures.h to remember what PDCM
stands for.
printf("Perf/Debug Capabilities MSR isn't supported\n");
> + return report_summary();
> + }
> +
> + perf_cap = rdmsr(MSR_IA32_PERF_CAPABILITIES);
> +
> if (!(perf_cap & PMU_CAP_LBR_FMT)) {
> printf("No LBR is detected!\n");
Similar complaint,
printf("Architectural LBRs are not supported.\n");
> return report_summary();
> --
> 2.31.1
>
