Messages in this thread | | | Date | Thu, 9 Nov 2023 15:43:07 +0800 | Subject | Re: [PATCH v7 14/19] KVM: selftests: Expand PMU counters test to verify LLC events | From | "Mi, Dapeng" <> |
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On 11/8/2023 8:31 AM, Sean Christopherson wrote: > Expand the PMU counters test to verify that LLC references and misses have > non-zero counts when the code being executed while the LLC event(s) is > active is evicted via CFLUSH{,OPT}. Note, CLFLUSH{,OPT} requires a fence > of some kind to ensure the cache lines are flushed before execution > continues. Use MFENCE for simplicity (performance is not a concern). > > Suggested-by: Jim Mattson <jmattson@google.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > .../selftests/kvm/x86_64/pmu_counters_test.c | 59 +++++++++++++------ > 1 file changed, 40 insertions(+), 19 deletions(-) > > diff --git a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c > index b9c073d3ade9..90381382c51f 100644 > --- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c > +++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c > @@ -14,9 +14,9 @@ > /* > * Number of "extra" instructions that will be counted, i.e. the number of > * instructions that are needed to set up the loop and then disabled the > - * counter. 2 MOV, 2 XOR, 1 WRMSR. > + * counter. 1 CLFLUSH/CLFLUSHOPT/NOP, 1 MFENCE, 2 MOV, 2 XOR, 1 WRMSR. > */ > -#define NUM_EXTRA_INSNS 5 > +#define NUM_EXTRA_INSNS 7 > #define NUM_INSNS_RETIRED (NUM_BRANCHES + NUM_EXTRA_INSNS) > > static uint8_t kvm_pmu_version; > @@ -107,6 +107,12 @@ static void guest_assert_event_count(uint8_t idx, > case INTEL_ARCH_BRANCHES_RETIRED_INDEX: > GUEST_ASSERT_EQ(count, NUM_BRANCHES); > break; > + case INTEL_ARCH_LLC_REFERENCES_INDEX: > + case INTEL_ARCH_LLC_MISSES_INDEX: > + if (!this_cpu_has(X86_FEATURE_CLFLUSHOPT) && > + !this_cpu_has(X86_FEATURE_CLFLUSH)) > + break; > + fallthrough; > case INTEL_ARCH_CPU_CYCLES_INDEX: > case INTEL_ARCH_REFERENCE_CYCLES_INDEX: > GUEST_ASSERT_NE(count, 0); > @@ -123,29 +129,44 @@ static void guest_assert_event_count(uint8_t idx, > GUEST_ASSERT_EQ(_rdpmc(pmc), 0xdead); > } > > +/* > + * Enable and disable the PMC in a monolithic asm blob to ensure that the > + * compiler can't insert _any_ code into the measured sequence. Note, ECX > + * doesn't need to be clobbered as the input value, @pmc_msr, is restored > + * before the end of the sequence. > + * > + * If CLFUSH{,OPT} is supported, flush the cacheline containing (at least) the > + * start of the loop to force LLC references and misses, i.e. to allow testing > + * that those events actually count. > + */ > +#define GUEST_MEASURE_EVENT(_msr, _value, clflush) \ > +do { \ > + __asm__ __volatile__("wrmsr\n\t" \ > + clflush "\n\t" \ > + "mfence\n\t" \ > + "1: mov $" __stringify(NUM_BRANCHES) ", %%ecx\n\t" \ > + "loop .\n\t" \ > + "mov %%edi, %%ecx\n\t" \ > + "xor %%eax, %%eax\n\t" \ > + "xor %%edx, %%edx\n\t" \ > + "wrmsr\n\t" \ > + :: "a"((uint32_t)_value), "d"(_value >> 32), \ > + "c"(_msr), "D"(_msr) \ > + ); \ > +} while (0) > + > static void __guest_test_arch_event(uint8_t idx, struct kvm_x86_pmu_feature event, > uint32_t pmc, uint32_t pmc_msr, > uint32_t ctrl_msr, uint64_t ctrl_msr_value) > { > wrmsr(pmc_msr, 0); > > - /* > - * Enable and disable the PMC in a monolithic asm blob to ensure that > - * the compiler can't insert _any_ code into the measured sequence. > - * Note, ECX doesn't need to be clobbered as the input value, @pmc_msr, > - * is restored before the end of the sequence. > - */ > - __asm__ __volatile__("wrmsr\n\t" > - "mov $" __stringify(NUM_BRANCHES) ", %%ecx\n\t" > - "loop .\n\t" > - "mov %%edi, %%ecx\n\t" > - "xor %%eax, %%eax\n\t" > - "xor %%edx, %%edx\n\t" > - "wrmsr\n\t" > - :: "a"((uint32_t)ctrl_msr_value), > - "d"(ctrl_msr_value >> 32), > - "c"(ctrl_msr), "D"(ctrl_msr) > - ); > + if (this_cpu_has(X86_FEATURE_CLFLUSHOPT)) > + GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "clflushopt 1f"); > + else if (this_cpu_has(X86_FEATURE_CLFLUSH)) > + GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "clflush 1f"); > + else > + GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "nop"); > > guest_assert_event_count(idx, event, pmc, pmc_msr); > }
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
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