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

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Message-ID: <7c6fde51-add4-35eb-fcff-bad847b85010@intel.com>
Date:   Thu, 8 Jul 2021 16:52:17 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     pbonzini@...hat.com, bp@...en8.de, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, weijiang.yang@...el.com,
        kan.liang@...ux.intel.com, ak@...ux.intel.com,
        wei.w.wang@...el.com, eranian@...gle.com, liuxiangdong5@...wei.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        like.xu.linux@...il.com, Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH V7 15/18] KVM: x86/pmu: Disable guest PEBS temporarily in
 two rare situations



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.
>
>> +	}
>> +}