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References: <20210310152333.1291338-1-ak@linux.intel.com>
In-Reply-To: <20210310152333.1291338-1-ak@linux.intel.com>
From:   Jim Mattson <jmattson@google.com>
Date:   Wed, 10 Mar 2021 07:35:58 -0800
Message-ID: <CALMp9eQ9yV0Q_Op5U6M0xuPcq5cDZZFAG+tDqBL3J=Kk6Z1ekw@mail.gmail.com>
Subject: Re: [PATCH] perf/x86/kvm: Fix inverted pebs_no_isolation check
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Mar 10, 2021 at 7:24 AM Andi Kleen <ak@linux.intel.com> wrote:
>
> The pebs_no_isolation optimization check is inverted. We want to disable
> PEBS isolation when the microcode is at least the revision in the table,
> not for older microcode. So remove the extra !.
The original code was correct because of the double negative. A "good"
CPU _has_ PEBS isolation. It's bad to have pebs_no_isolation.