From: Sean Christopherson <seanjc@google.com>
To: Jim Mattson <jmattson@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
the arch/x86 maintainers <x86@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>,
LKML <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>, Like Xu <like.xu@linux.intel.com>,
Dmitry Vyukov <dvyukov@google.com>,
syzbot+cce9ef2dd25246f815ee@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] x86/perf: Use RET0 as default for guest_get_msrs to handle "no PMU" case
Date: Tue, 9 Mar 2021 11:46:18 -0800 [thread overview]
Message-ID: <YEfQir8rv8/j2hgn@google.com> (raw)
In-Reply-To: <CALMp9eRL4QRq4-DKEveNsJ8b2XSYEhZ-zKGFWsCcoZMnDeRtxg@mail.gmail.com>
On Tue, Mar 09, 2021, Jim Mattson wrote:
> On Tue, Mar 9, 2021 at 9:10 AM Sean Christopherson <seanjc@google.com>
> wrote:
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 50810d471462..32cf8287d4a7 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6580,8 +6580,8 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx
> > *vmx)
> > int i, nr_msrs;
> > struct perf_guest_switch_msr *msrs;
> >
> > + /* Note, nr_msrs may be garbage if perf_guest_get_msrs() returns
> > NULL. */
> >
>
> You could drop the scary comment with a profligate initialization of
> nr_msrs to 0.
Yeah, I considered that as well. I opted for the scary comment because I
wanted to dissuade future patches from modifying this code without taking into
account the non-obvious behavior.
next prev parent reply other threads:[~2021-03-09 19:47 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-09 17:10 [PATCH v2] x86/perf: Use RET0 as default for guest_get_msrs to handle "no PMU" case Sean Christopherson
2021-03-09 18:26 ` Jim Mattson
[not found] ` <CALMp9eRL4QRq4-DKEveNsJ8b2XSYEhZ-zKGFWsCcoZMnDeRtxg@mail.gmail.com>
2021-03-09 19:46 ` Sean Christopherson [this message]
2021-03-10 8:18 ` Peter Zijlstra
2021-03-10 18:16 ` Sean Christopherson
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