Re: [PATCH V9 00/18] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 7/28/2021 11:45 PM, Peter Zijlstra wrote:
> On Thu, Jul 22, 2021 at 01:41:41PM +0800, Zhu Lingshan wrote:
>> The guest Precise Event Based Sampling (PEBS) feature can provide an
>> architectural state of the instruction executed after the guest instruction
>> that exactly caused the event. It needs new hardware facility only available
>> on Intel Ice Lake Server platforms. This patch set enables the basic PEBS
>> feature for KVM guests on ICX.
>>
>> We can use PEBS feature on the Linux guest like native:
>>
>>     # echo 0 > /proc/sys/kernel/watchdog (on the host)
>>     # perf record -e instructions:ppp ./br_instr a
>>     # perf record -c 100000 -e instructions:pp ./br_instr a
> Why does the host need to disable the watchdog? IIRC ICL has multiple
> PEBS capable counters. Also, I think the watchdog ends up on a fixed
> counter by default anyway.
>
>> Like Xu (17):
>>    perf/core: Use static_call to optimize perf_guest_info_callbacks
>>    perf/x86/intel: Add EPT-Friendly PEBS for Ice Lake Server
>>    perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest
>>    perf/x86/core: Pass "struct kvm_pmu *" to determine the guest values
>>    KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled
>>    KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter
>>    KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS
>>    KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter
>>    KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter
>>    KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to support guest DS
>>    KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS
>>    KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled
>>    KVM: x86/pmu: Move pmc_speculative_in_use() to arch/x86/kvm/pmu.h
>>    KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations
>>    KVM: x86/pmu: Add kvm_pmu_cap to optimize perf_get_x86_pmu_capability
>>    KVM: x86/cpuid: Refactor host/guest CPU model consistency check
>>    KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64
>>
>> Peter Zijlstra (Intel) (1):
>>    x86/perf/core: Add pebs_capable to store valid PEBS_COUNTER_MASK value
> Looks good:
>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> How do we want to route this, all through the KVM tree?
I will send a V10 patchset then ping Paolo.
>
> One little nit I had; would something like the below (on top perhaps)
> make the code easier to read?
V10 will include this change.

Thanks,
Zhu Lingshan
>
> ---
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3921,9 +3921,12 @@ static struct perf_guest_switch_msr *int
>   	struct kvm_pmu *kvm_pmu = (struct kvm_pmu *)data;
>   	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
>   	u64 pebs_mask = cpuc->pebs_enabled & x86_pmu.pebs_capable;
> +	int global_ctrl, pebs_enable;
>   
>   	*nr = 0;
> -	arr[(*nr)++] = (struct perf_guest_switch_msr){
> +
> +	global_ctrl = (*nr)++;
> +	arr[global_ctrl] = (struct perf_guest_switch_msr){
>   		.msr = MSR_CORE_PERF_GLOBAL_CTRL,
>   		.host = intel_ctrl & ~cpuc->intel_ctrl_guest_mask,
>   		.guest = intel_ctrl & (~cpuc->intel_ctrl_host_mask | ~pebs_mask),
> @@ -3966,23 +3969,23 @@ static struct perf_guest_switch_msr *int
>   		};
>   	}
>   
> -	arr[*nr] = (struct perf_guest_switch_msr){
> +	pebs_enable = (*nr)++;
> +	arr[pebs_enable] = (struct perf_guest_switch_msr){
>   		.msr = MSR_IA32_PEBS_ENABLE,
>   		.host = cpuc->pebs_enabled & ~cpuc->intel_ctrl_guest_mask,
>   		.guest = pebs_mask & ~cpuc->intel_ctrl_host_mask,
>   	};
>   
> -	if (arr[*nr].host) {
> +	if (arr[pebs_enable].host) {
>   		/* Disable guest PEBS if host PEBS is enabled. */
> -		arr[*nr].guest = 0;
> +		arr[pebs_enable].guest = 0;
>   	} else {
>   		/* Disable guest PEBS for cross-mapped PEBS counters. */
> -		arr[*nr].guest &= ~kvm_pmu->host_cross_mapped_mask;
> +		arr[pebs_enable].guest &= ~kvm_pmu->host_cross_mapped_mask;
>   		/* Set hw GLOBAL_CTRL bits for PEBS counter when it runs for guest */
> -		arr[0].guest |= arr[*nr].guest;
> +		arr[global_ctrl].guest |= arr[pebs_enable].guest;
>   	}
>   
> -	++(*nr);
>   	return arr;
>   }
>   
>
>
>