From: Sean Christopherson <seanjc@google.com>
To: Mingwei Zhang <mizhang@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Dapeng Mi <dapeng1.mi@intel.com>,
Jim Mattson <jmattson@google.com>, Like Xu <likexu@tencent.com>
Subject: Re: [PATCH] KVM: vPMU: Use atomic bit operations for global_status
Date: Mon, 11 Sep 2023 18:09:49 +0000 [thread overview]
Message-ID: <ZP9X7YvstWhS/pWn@google.com> (raw)
In-Reply-To: <CAL715WKyS4sTH3yEOX2OyV+fxMLMOAV6tX-A7fvEAKEUGj8uxw@mail.gmail.com>
On Mon, Sep 11, 2023, Mingwei Zhang wrote:
> On Mon, Sep 11, 2023 at 8:01 AM Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Mon, Sep 11, 2023, Mingwei Zhang wrote:
> > > Use atomic bit operations for pmu->global_status because it may suffer from
> > > race conditions between emulated overflow in KVM vPMU and PEBS overflow in
> > > host PMI handler.
> >
> > Only if the host PMI occurs on a different pCPU, and if that can happen don't we
> > have a much larger problem?
>
> Why on different pCPU? For vPMU, I think there is always contention
> between the vCPU thread and the host PMI handler running on the same
> pCPU, no?
A non-atomic instruction can't be interrupted by an NMI, or any other event, so
I don't see how switching to atomic operations fixes anything unless the NMI comes
in on a different pCPU.
next prev parent reply other threads:[~2023-09-11 20:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-11 6:11 [PATCH] KVM: vPMU: Use atomic bit operations for global_status Mingwei Zhang
2023-09-11 15:01 ` Sean Christopherson
2023-09-11 18:00 ` Mingwei Zhang
2023-09-11 18:09 ` Sean Christopherson [this message]
2023-09-11 23:42 ` Mingwei Zhang
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