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

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Date:   Fri, 30 Jun 2023 07:28:29 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Roman Kagan <rkagan@...zon.de>, Jim Mattson <jmattson@...gle.com>,
        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>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH] KVM: x86: vPMU: truncate counter value to allowed width

On Fri, Jun 30, 2023, Roman Kagan wrote:
> On Thu, Jun 29, 2023 at 05:11:06PM -0700, Sean Christopherson wrote:
> > @@ -74,6 +74,14 @@ static inline u64 pmc_read_counter(struct kvm_pmc *pmc)
> >         return counter & pmc_bitmask(pmc);
> >  }
> > 
> > +static inline void pmc_write_counter(struct kvm_pmc *pmc, u64 val)
> > +{
> > +       if (pmc->perf_event && !pmc->is_paused)
> > +               perf_event_set_count(pmc->perf_event, val);
> > +
> > +       pmc->counter = val;
> 
> Doesn't this still have the original problem of storing wider value than
> allowed?

Yes, this was just to fix the counter offset weirdness.  My plan is to apply your
patch on top.  Sorry for not making that clear.