Re: [PATCH v5 06/16] KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter

[Xu, Like]

On 2021/4/19 16:11, Liuxiangdong wrote:
> On 2021/4/15 11:20, Like Xu wrote:
> > When a guest counter is configured as a PEBS counter through
> > IA32_PEBS_ENABLE, a guest PEBS event will be reprogrammed by
> > configuring a non-zero precision level in the perf_event_attr.
> >
> > The guest PEBS overflow PMI bit would be set in the guest
> > GLOBAL_STATUS MSR when PEBS facility generates a PEBS
> > overflow PMI based on guest IA32_DS_AREA MSR.
> >
> > Even with the same counter index and the same event code and
> > mask, guest PEBS events will not be reused for non-PEBS events.
> >
> > Originally-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Co-developed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/pmu.c | 34 ++++++++++++++++++++++++++++++++--
> >   1 file changed, 32 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index 827886c12c16..0f86c1142f17 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -74,11 +74,21 @@ static void kvm_perf_overflow_intr(struct perf_event 
> > *perf_event,
> >   {
> >       struct kvm_pmc *pmc = perf_event->overflow_handler_context;
> >       struct kvm_pmu *pmu = pmc_to_pmu(pmc);
> > +    bool skip_pmi = false;
> >         if (!test_and_set_bit(pmc->idx, pmu->reprogram_pmi)) {
> > -        __set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
> > +        if (perf_event->attr.precise_ip) {
> > +            /* Indicate PEBS overflow PMI to guest. */
> > +            skip_pmi = __test_and_set_bit(GLOBAL_STATUS_BUFFER_OVF_BIT,
> > +                              (unsigned long *)&pmu->global_status);
> > +        } else {
> > +            __set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
> > +        }
> >           kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
> >   +        if (skip_pmi)
> > +            return;
> > +
> >           /*
> >            * Inject PMI. If vcpu was in a guest mode during NMI PMI
> >            * can be ejected on a guest mode re-entry. Otherwise we can't
> > @@ -99,6 +109,7 @@ static void pmc_reprogram_counter(struct kvm_pmc 
> > *pmc, u32 type,
> >                     bool exclude_kernel, bool intr,
> >                     bool in_tx, bool in_tx_cp)
> >   {
> > +    struct kvm_pmu *pmu = vcpu_to_pmu(pmc->vcpu);
> >       struct perf_event *event;
> >       struct perf_event_attr attr = {
> >           .type = type,
> > @@ -110,6 +121,7 @@ static void pmc_reprogram_counter(struct kvm_pmc 
> > *pmc, u32 type,
> >           .exclude_kernel = exclude_kernel,
> >           .config = config,
> >       };
> > +    bool pebs = test_bit(pmc->idx, (unsigned long *)&pmu->pebs_enable);
>
> pebs_enable is defined in patch 07, but used here(in patch 06).
> Maybe we can change the patches order in next patch version if necessary.

Thanks! I'll fix it.

> >       attr.sample_period = get_sample_period(pmc, pmc->counter);
> >   @@ -124,9 +136,23 @@ static void pmc_reprogram_counter(struct kvm_pmc 
> > *pmc, u32 type,
> >           attr.sample_period = 0;
> >           attr.config |= HSW_IN_TX_CHECKPOINTED;
> >       }
> > +    if (pebs) {
> > +        /*
> > +         * The non-zero precision level of guest event makes the ordinary
> > +         * guest event becomes a guest PEBS event and triggers the host
> > +         * PEBS PMI handler to determine whether the PEBS overflow PMI
> > +         * comes from the host counters or the guest.
> > +         *
> > +         * For most PEBS hardware events, the difference in the software
> > +         * precision levels of guest and host PEBS events will not affect
> > +         * the accuracy of the PEBS profiling result, because the 
> > "event IP"
> > +         * in the PEBS record is calibrated on the guest side.
> > +         */
> > +        attr.precise_ip = 1;
> > +    }
> >         event = perf_event_create_kernel_counter(&attr, -1, current,
> > -                         intr ? kvm_perf_overflow_intr :
> > +                         (intr || pebs) ? kvm_perf_overflow_intr :
> >                            kvm_perf_overflow, pmc);
> >       if (IS_ERR(event)) {
> >           pr_debug_ratelimited("kvm_pmu: event creation failed %ld for 
> > pmc->idx = %d\n",
> > @@ -161,6 +187,10 @@ static bool pmc_resume_counter(struct kvm_pmc *pmc)
> >                     get_sample_period(pmc, pmc->counter)))
> >           return false;
> >   +    if (!test_bit(pmc->idx, (unsigned long 
> > *)&pmc_to_pmu(pmc)->pebs_enable) &&
> > +        pmc->perf_event->attr.precise_ip)
> > +        return false;
> > +
> >       /* reuse perf_event to serve as pmc_reprogram_counter() does*/
> >       perf_event_enable(pmc->perf_event);