linux-kernel - Re: [PATCH] KVM: x86: vPMU: truncate counter value to allowed width

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Message-ID: <CAL715WJfOXOovUJSBtC0SfXVTuXEXwRF3sQBUzGaPDXe99dRoQ@mail.gmail.com>
Date:   Fri, 30 Jun 2023 11:03:34 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Roman Kagan <rkagan@...zon.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Eric Hankland <ehankland@...gle.com>, kvm@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Like Xu <likexu@...cent.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] KVM: x86: vPMU: truncate counter value to allowed width

> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 48a0528080ab..8d28158e58f2 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -322,7 +322,7 @@ static void reprogram_counter(struct kvm_pmc *pmc)
>         if (!pmc_event_is_allowed(pmc))
>                 goto reprogram_complete;
>
> -       if (pmc->counter < pmc->prev_counter)
> +       if (pmc->counter == 0)
>                 __kvm_perf_overflow(pmc, false);
>
>         if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL)
>
> Since this is software emulation, we (KVM) should only handle overflow
> by plusing one?

Sign. Please ignore this as it is not only hacky but also not working.