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

[Zhu, Lingshan]

On 7/2/2021 8:46 PM, Peter Zijlstra wrote:
> 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?
Hi Peter,

We expect to handle these cases in the "slow path" series, try to 
cross-map the counters.

Thanks!
> > +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.
>
> > +	}
> > +}