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Subject: Re: [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable
 guest PEBS via DS
To:     "Xu, Like" <like.xu@intel.com>
References: <20210511024214.280733-1-like.xu@linux.intel.com>
 <609FA2B7.7030801@huawei.com>
 <868a0ed9-d4a5-c135-811e-a3420b7913ac@linux.intel.com>
 <60A3B1DC.7000002@huawei.com>
 <a65c8556-4eac-b8db-8aa4-98229f47fc8d@intel.com>
CC:     Borislav Petkov <bp@alien8.de>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, <weijiang.yang@intel.com>,
        Kan Liang <kan.liang@linux.intel.com>, <ak@linux.intel.com>,
        <wei.w.wang@intel.com>, <eranian@google.com>,
        <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        <kvm@vger.kernel.org>, "Fangyi (Eric)" <eric.fangyi@huawei.com>,
        Xiexiangyou <xiexiangyou@huawei.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paolo Bonzini" <pbonzini@redhat.com>,
        Like Xu <like.xu@linux.intel.com>
From:   Liuxiangdong <liuxiangdong5@huawei.com>
Message-ID: <60A46D78.3000205@huawei.com>
Date:   Wed, 19 May 2021 09:44:24 +0800
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On 2021/5/18 20:40, Xu, Like wrote:
> On 2021/5/18 20:23, Liuxiangdong wrote:
>>
>>
>> On 2021/5/17 14:38, Like Xu wrote:
>>> Hi xiangdong,
>>>
>>> On 2021/5/15 18:30, Liuxiangdong wrote:
>>>>
>>>>
>>>> On 2021/5/11 10:41, Like Xu wrote:
>>>>> A new kernel cycle has begun, and this version looks promising.
>>>>>
>>>>> 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:
>>>>>
>>>>>    # perf record -e instructions:ppp ./br_instr a
>>>>>    # perf record -c 100000 -e instructions:pp ./br_instr a
>>>>
>>>> Hi, Like.
>>>> Has the qemu patch been modified?
>>>>
>>>> https://lore.kernel.org/kvm/f4dcb068-2ddf-428f-50ad-39f65cad3710@intel.com/ 
>>>> ?
>>>
>>> I think the qemu part still works based on
>>> 609d7596524ab204ccd71ef42c9eee4c7c338ea4 (tag: v6.0.0).
>>>
>>
>> Yes. I applied these two qemu patches to qemu v6.0.0 and this kvm 
>> patches set to latest kvm tree.
>>
>> I can see pebs flags in Guest(linux 5.11) on the IceLake( Model: 106  
>> Model name: Intel(R) Xeon(R) Platinum 8378A CPU),
>> and i can use PEBS like this.
>>
>>     #perf record -e instructions:pp
>>
>> It can work normally.
>>
>> But  there is no sampling when i use "perf record -e events:pp" or 
>> just "perf record" in guest
>> unless i delete patch 09 and patch 13 from this kvm patches set.
>>
>>
>
> With patch 9 and 13, does the basic counter sampling still work ?
> You may retry w/ "echo 0 > /proc/sys/kernel/watchdog" on the host and 
> guest.
>

In fact, I didn't use "echo 0 > /proc/sys/kernel/watchdog" when I tried 
PEBS patches V3 on Icelake.
Why should we use it now?  What does it have to do with sampling?

Thanks!

>> Have you tried "perf record -e events:pp" in this patches set? Does 
>> it work normally?
>
> All my PEBS testcases passed. You may dump guest msr traces from your 
> testcase with me.
>
>>
>>
>>
>> Thanks!
>> Xiangdong Liu
>>
>>
>>
>>> When the LBR qemu patch receives the ACK from the maintainer,
>>> I will submit PBES qemu support because their changes are very similar.
>>>
>>> Please help review this version and
>>> feel free to add your comments or "Reviewed-by".
>>>
>>> Thanks,
>>> Like Xu
>>>
>>>>
>>>>
>>>>> To emulate guest PEBS facility for the above perf usages,
>>>>> we need to implement 2 code paths:
>>>>>
>>>>> 1) Fast path
>>>>>
>>>>> This is when the host assigned physical PMC has an identical index as
>>>>> the virtual PMC (e.g. using physical PMC0 to emulate virtual PMC0).
>>>>> This path is used in most common use cases.
>>>>>
>>>>> 2) Slow path
>>>>>
>>>>> This is when the host assigned physical PMC has a different index
>>>>> from the virtual PMC (e.g. using physical PMC1 to emulate virtual 
>>>>> PMC0)
>>>>> In this case, KVM needs to rewrite the PEBS records to change the
>>>>> applicable counter indexes to the virtual PMC indexes, which would
>>>>> otherwise contain the physical counter index written by PEBS 
>>>>> facility,
>>>>> and switch the counter reset values to the offset corresponding to
>>>>> the physical counter indexes in the DS data structure.
>>>>>
>>>>> The previous version [0] enables both fast path and slow path, which
>>>>> seems a bit more complex as the first step. In this patchset, we want
>>>>> to start with the fast path to get the basic guest PEBS enabled while
>>>>> keeping the slow path disabled. More focused discussion on the slow
>>>>> path [1] is planned to be put to another patchset in the next step.
>>>>>
>>>>> Compared to later versions in subsequent steps, the functionality
>>>>> to support host-guest PEBS both enabled and the functionality to
>>>>> emulate guest PEBS when the counter is cross-mapped are missing
>>>>> in this patch set (neither of these are typical scenarios).
>>>>>
>>>>> With the basic support, the guest can retrieve the correct PEBS
>>>>> information from its own PEBS records on the Ice Lake servers.
>>>>> And we expect it should work when migrating to another Ice Lake
>>>>> and no regression about host perf is expected.
>>>>>
>>>>> Here are the results of pebs test from guest/host for same workload:
>>>>>
>>>>> perf report on guest:
>>>>> # Samples: 2K of event 'instructions:ppp', # Event count 
>>>>> (approx.): 1473377250
>>>>> # Overhead  Command   Shared Object      Symbol
>>>>>    57.74%  br_instr  br_instr           [.] lfsr_cond
>>>>>    41.40%  br_instr  br_instr           [.] cmp_end
>>>>>     0.21%  br_instr  [kernel.kallsyms]  [k] __lock_acquire
>>>>>
>>>>> perf report on host:
>>>>> # Samples: 2K of event 'instructions:ppp', # Event count 
>>>>> (approx.): 1462721386
>>>>> # Overhead  Command   Shared Object     Symbol
>>>>>    57.90%  br_instr  br_instr          [.] lfsr_cond
>>>>>    41.95%  br_instr  br_instr          [.] cmp_end
>>>>>     0.05%  br_instr  [kernel.vmlinux]  [k] lock_acquire
>>>>>     Conclusion: the profiling results on the guest are similar 
>>>>> tothat on the host.
>>>>>
>>>>> A minimum guest kernel version may be v5.4 or a backport version
>>>>> support Icelake server PEBS.
>>>>>
>>>>> Please check more details in each commit and feel free to comment.
>>>>>
>>>>> Previous:
>>>>> https://lore.kernel.org/kvm/20210415032016.166201-1-like.xu@linux.intel.com/ 
>>>>>
>>>>>
>>>>> [0] 
>>>>> https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/
>>>>> [1] 
>>>>> https://lore.kernel.org/kvm/20210115191113.nktlnmivc3edstiv@two.firstfloor.org/ 
>>>>>
>>>>>
>>>>> V5 -> V6 Changelog:
>>>>> - Rebased on the latest kvm/queue tree;
>>>>> - Fix a git rebase issue (Liuxiangdong);
>>>>> - Adjust the patch sequence 06/07 for bisection (Liuxiangdong);
>>>>>
>>>>> Like Xu (16):
>>>>>    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: 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: Adjust precise_ip to emulate Ice Lake guest PDIR 
>>>>> counter
>>>>>    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
>>>>>
>>>>>   arch/x86/events/core.c            |   5 +-
>>>>>   arch/x86/events/intel/core.c      | 129 
>>>>> ++++++++++++++++++++++++------
>>>>>   arch/x86/events/perf_event.h      |   5 +-
>>>>>   arch/x86/include/asm/kvm_host.h   |  16 ++++
>>>>>   arch/x86/include/asm/msr-index.h  |   6 ++
>>>>>   arch/x86/include/asm/perf_event.h |   5 +-
>>>>>   arch/x86/kvm/cpuid.c              |  24 ++----
>>>>>   arch/x86/kvm/cpuid.h              |   5 ++
>>>>>   arch/x86/kvm/pmu.c                |  50 +++++++++---
>>>>>   arch/x86/kvm/pmu.h                |  38 +++++++++
>>>>>   arch/x86/kvm/vmx/capabilities.h   |  26 ++++--
>>>>>   arch/x86/kvm/vmx/pmu_intel.c      | 115 +++++++++++++++++++++-----
>>>>>   arch/x86/kvm/vmx/vmx.c            |  24 +++++-
>>>>>   arch/x86/kvm/vmx/vmx.h            |   2 +-
>>>>>   arch/x86/kvm/x86.c                |  14 ++--
>>>>>   15 files changed, 368 insertions(+), 96 deletions(-)
>>>>>
>>>
>>
>