linux-kernel - [PATCH v2 0/7] KVM: x86: Intel PERF

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Date:   Wed,  3 Aug 2022 19:26:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
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: [PATCH v2 0/7] KVM: x86: Intel PERF_CAPABILITIES fixes and cleanups

Bug fixes and cleanups related to KVM's handling of PERF_CAPABILITIES.

Bug #1 - Refresh KVM's vPMU after userspace writes PERF_CAPABILITIES, and
then leverage that fix to avoiding checking guest_cpuid_has(X86_FEATURE_PDCM)
during VM-Enter, which is slow enough that it shows up in perf traces[*].

Bug #2 - Don't advertise 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 patches remove unnecessary stubs and unreachable error paths,
which allows for a cleaner fix for bug #2.

[*] https://gist.github.com/avagin/f50a6d569440c9ae382281448c187f4e

v2:
 - 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 (7):
  KVM: x86: Refresh PMU after writes to MSR_IA32_PERF_CAPABILITIES
  perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers
  perf/x86/core: Drop the unnecessary return value from
    x86_perf_get_lbr()
  KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs
  KVM: VMX: Use proper type-safe functions for vCPU => LBRs helpers
  KVM: VMX: Adjust number of LBR records for PERF_CAPABILITIES at
    refresh
  KVM: VMX: Simplify capability check when handling PERF_CAPABILITIES
    write

 arch/x86/events/intel/lbr.c       |  6 +---
 arch/x86/include/asm/perf_event.h | 55 ++++++++-----------------------
 arch/x86/kvm/vmx/capabilities.h   |  5 ++-
 arch/x86/kvm/vmx/pmu_intel.c      | 12 ++-----
 arch/x86/kvm/vmx/vmx.c            |  6 ++--
 arch/x86/kvm/vmx/vmx.h            | 53 +++++++++++++++++------------
 arch/x86/kvm/x86.c                |  4 +--
 7 files changed, 58 insertions(+), 83 deletions(-)


base-commit: 93472b79715378a2386598d6632c654a2223267b
-- 
2.37.1.559.g78731f0fdb-goog