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

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