linux-kernel - Re: [PATCH 0/6] KVM: x86/pmu: Clean up emulated PMC event handling

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Date:   Wed, 1 Nov 2023 17:37:15 +0800
From:   "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mingwei Zhang <mizhang@...gle.com>,
        Roman Kagan <rkagan@...zon.de>,
        Jim Mattson <jmattson@...gle.com>,
        Like Xu <like.xu.linux@...il.com>
Subject: Re: [PATCH 0/6] KVM: x86/pmu: Clean up emulated PMC event handling


On 10/24/2023 7:39 AM, Sean Christopherson wrote:
> The ultimate goal of this series is to track emulated counter events using
> a dedicated variable instead of trying to track the previous counter value.
> Tracking the previous counter value is flawed as it takes a snapshot at
> every emulated event, but only checks for overflow prior to VM-Enter, i.e.
> KVM could miss an overflow if KVM ever supports emulating event types that
> can occur multiple times in a single VM-Exit.
>
> Patches 1-5 are (some loosely, some tightly) related fixes and cleanups to
> simplify the emulated counter approach implementation.  The fixes are
> tagged for stable as usersepace could cause some weirdness around perf
> events, but I doubt any real world VMM is actually affected.
>
> Sean Christopherson (6):
>    KVM: x86/pmu: Move PMU reset logic to common x86 code
>    KVM: x86/pmu: Reset the PMU, i.e. stop counters, before refreshing
>    KVM: x86/pmu: Stop calling kvm_pmu_reset() at RESET (it's redundant)
>    KVM: x86/pmu: Remove manual clearing of fields in kvm_pmu_init()
>    KVM: x86/pmu: Update sample period in pmc_write_counter()
>    KVM: x86/pmu: Track emulated counter events instead of previous
>      counter
>
>   arch/x86/include/asm/kvm-x86-pmu-ops.h |   2 +-
>   arch/x86/include/asm/kvm_host.h        |  17 +++-
>   arch/x86/kvm/pmu.c                     | 128 +++++++++++++++++++++----
>   arch/x86/kvm/pmu.h                     |  47 +--------
>   arch/x86/kvm/svm/pmu.c                 |  17 ----
>   arch/x86/kvm/vmx/pmu_intel.c           |  22 -----
>   arch/x86/kvm/x86.c                     |   1 -
>   7 files changed, 127 insertions(+), 107 deletions(-)
>
>
> base-commit: ec2f1daad460c6201338dae606466220ccaa96d5

Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>