On 6/17/2022 2:34 AM, Sean Christopherson wrote:
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))
...
Oops, this is more x86 style code, thank you!
+ 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");
Exactly, I'll bear it in mind :-)
+ 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");
Sure.
return report_summary();
--
2.31.1
