Re: [PATCH V7 15/18] KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations

Peter Zijlstra
2021-07-02T12:47:22Z

On Tue, Jun 22, 2021 at 05:43:03PM +0800, Zhu Lingshan wrote:
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 22386c1a32b4..8bf494f8af3e 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3970,8 +3970,15 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)
> .guest = pebs_mask & ~cpuc->intel_ctrl_host_mask,
> };
>
> - /* Set hw GLOBAL_CTRL bits for PEBS counter when it runs for guest */
> - arr[0].guest |= arr[*nr].guest;
> + if (arr[*nr].host) {
> + /* Disable guest PEBS if host PEBS is enabled. */
> + arr[*nr].guest = 0;
> + } else {
> + /* Disable guest PEBS for cross-mapped PEBS counters. */
> + arr[*nr].guest &= ~pmu->host_cross_mapped_mask;
> + /* Set hw GLOBAL_CTRL bits for PEBS counter when it runs for guest */
> + arr[0].guest |= arr[*nr].guest;
> + }

Not saying I disagree, but is there any way for the guest to figure out
why things aren't working? Is there like a guest log we can dump
something in?

> +void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu)
> +{
> + struct kvm_pmc *pmc = NULL;
> + int bit;
> +
> + for_each_set_bit(bit, (unsigned long *)&pmu->global_ctrl,
> + X86_PMC_IDX_MAX) {
> + pmc = kvm_x86_ops.pmu_ops->pmc_idx_to_pmc(pmu, bit);
> +
> + if (!pmc || !pmc_speculative_in_use(pmc) ||
> + !pmc_is_enabled(pmc))
> + continue;
> +
> + if (pmc->perf_event && (pmc->idx != pmc->perf_event->hw.idx))
> + pmu->host_cross_mapped_mask |=
> + BIT_ULL(pmc->perf_event->hw.idx);

{ } again.

> + }
> +}