linux-kernel - Re: [PATCH] perf, x86: Optimize intel_pmu_pebs_fixup

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Message-ID: <CA+55aFwfsyofuZtNyUGKPWdvqc=4gOW=HTFPxsiM-3GS1G8KKQ@mail.gmail.com>
Date:	Wed, 23 Oct 2013 08:09:53 +0100
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Don Zickus <dzickus@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
	dave.hansen@...ux.intel.com, Stephane Eranian <eranian@...gle.com>,
	jmario@...hat.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] perf, x86: Optimize intel_pmu_pebs_fixup_ip()

On Tue, Oct 22, 2013 at 10:12 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> Careful! There is one magic piece of state that you need to
>> save-and-restore if you do this, namely %cr2. Taking a page fault
>> always writes to %cr2, and we must *not* corrupt it in the NMI
>> handler.
>
> It looks like this is already dealt with (a similar thing is done for
> i386).

Oh, ok then, we should be good to go. I wonder why we needed that
special "_nmi()" version, then..

Please do check that NMI increment the irq-counts etc.. Otherwise
you'll need to add the explicit "pagefault_disable/enable()" pair
around the __copy_from_user_inatomic()..

            Linus
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