From: Andi Kleen <ak@linux.intel.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>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Kan Liang <kan.liang@linux.intel.com>,
linux-kernel@vger.kernel.org, kvm-list@vger.kernel.org,
Peter Shier <pshier@google.com>
Subject: Re: [PATCH] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]
Date: Wed, 21 Apr 2021 19:05:12 -0700 [thread overview]
Message-ID: <20210422020512.GH1401198@tassilo.jf.intel.com> (raw)
In-Reply-To: <20210422001834.1748319-1-jmattson@google.com>
On Wed, Apr 21, 2021 at 05:18:34PM -0700, Jim Mattson wrote:
> The only stepping of Broadwell Xeon parts is stepping 1. Fix the
> relevant isolation_ucodes[] entry, which previously enumerated
> stepping 2.
>
> Although the original commit was characterized as an optimization, it
> is also a workaround for a correctness issue.
>
> If a PMI arrives between kvm's call to perf_guest_get_msrs() and the
> subsequent VM-entry, a stale value for the IA32_PEBS_ENABLE MSR may be
> restored at the next VM-exit. This is because, unbeknownst to kvm, PMI
> throttling may clear bits in the IA32_PEBS_ENABLE MSR. CPUs with "PEBS
> isolation" don't suffer from this issue, because perf_guest_get_msrs()
> doesn't report the IA32_PEBS_ENABLE value.
Acked-by: Andi Kleen <ak@linux.intel.com>
-Andi
next prev parent reply other threads:[~2021-04-22 2:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 0:18 [PATCH] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[] Jim Mattson
2021-04-22 2:05 ` Andi Kleen [this message]
2021-04-23 6:53 ` [tip: perf/urgent] " tip-bot2 for Jim Mattson
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