linux-kernel - Re: [PATCH v5 0/8] KVM: x86: Intel LBR related perf cleanups

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Date:   Wed, 2 Nov 2022 18:18:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Like Xu <like.xu.linux@...il.com>
Subject: Re: [PATCH v5 0/8] KVM: x86: Intel LBR related perf cleanups

On 10/6/22 02:03, Sean Christopherson wrote:
> PeterZ, I dropped your ACK from v4 because the perf patches were completely
> broken.
> 
> Fix a bug where KVM incorrectly advertises PMU_CAP_LBR_FMT to userspace if
> perf has disabled LBRs, e.g. because probing one or more LBR MSRs during
> setup hit a #GP.
> 
> The non-KVM patch cleans up a KVM-specific perf API to fix a benign bug
> where KVM ignores the error return from the API.
> 
> The remaining patches clean up KVM's PERF_CAPABILITIES mess, which makes
> everything far more complex than it needs to be by
> 
> v5:
>   - Drop perf patches that removed stubs.  The stubs are sadly necessary
>     when CPU_SUP_INTEL=n && KVM_INTEL={m,y}, which is possible due to
>     KVM_INTEL effectively depending on INTEL || CENTAUR || ZHAOXIN.
>     [hint provided by kernel test robot].
>   - Add a patch to ignore guest CPUID on host userspace MSR writes.
>   - Add supported PERF_CAPABILITIES to kvm_caps to simplify code for all
>     parties.
> 
> v4
>   - https://lore.kernel.org/all/20220901173258.925729-1-seanjc@google.com:
>   - Make vmx_get_perf_capabilities() non-inline to avoid references to
>     x86_perf_get_lbr() when CPU_SUP_INTEL=n. [kernel test robot]
> 
> v3:
>   - https://lore.kernel.org/all/20220831000051.4015031-1-seanjc@google.com
>   - Drop patches for bug #1 (already merged).
>   - Drop misguided "clean up the capability check" patch. [Like]
> 
> v2:
>   - https://lore.kernel.org/all/20220803192658.860033-1-seanjc@google.com
>   - Add patches to fix bug #2. [Like]
>   - Add a patch to clean up the capability check.
>   - Tweak the changelog for the PMU refresh bug fix to call out that
>     KVM should disallow changing feature MSRs after KVM_RUN. [Like]
> 
> v1: https://lore.kernel.org/all/20220727233424.2968356-1-seanjc@google.com
> 
> Sean Christopherson (8):
>    perf/x86/core: Zero @lbr instead of returning -1 in x86_perf_get_lbr()
>      stub
>    KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs
>    KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()
>    KVM: VMX: Ignore guest CPUID for host userspace writes to DEBUGCTL
>    KVM: x86: Track supported PERF_CAPABILITIES in kvm_caps
>    KVM: x86: Init vcpu->arch.perf_capabilities in common x86 code
>    KVM: x86: Handle PERF_CAPABILITIES in common x86's
>      kvm_get_msr_feature()
>    KVM: x86: Directly query supported PERF_CAPABILITIES for WRMSR checks
> 
>   arch/x86/events/intel/lbr.c       |  6 +---
>   arch/x86/include/asm/perf_event.h |  6 ++--
>   arch/x86/kvm/svm/svm.c            |  3 +-
>   arch/x86/kvm/vmx/capabilities.h   | 37 ----------------------
>   arch/x86/kvm/vmx/pmu_intel.c      |  1 -
>   arch/x86/kvm/vmx/vmx.c            | 51 +++++++++++++++++++++++--------
>   arch/x86/kvm/x86.c                | 14 ++++-----
>   arch/x86/kvm/x86.h                |  1 +
>   8 files changed, 52 insertions(+), 67 deletions(-)
> 
> 
> base-commit: e18d6152ff0f41b7f01f9817372022df04e0d354

Queued, with patches 2-4 destined to kvm/master.

Paolo