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Message-ID: <1337696825.13348.44.camel@gandalf.stny.rr.com>
Subject: Re: NMI vs #PF clash
From: Steven Rostedt <rostedt@goodmis.org>
To: Avi Kivity <avi@redhat.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Paul Turner <pjt@google.com>, Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 22 May 2012 10:27:05 -0400
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On Tue, 2012-05-22 at 17:20 +0300, Avi Kivity wrote:
> On 05/22/2012 05:09 PM, Steven Rostedt wrote:
> >> > 
> >> > Or we could just have the NMI always restore the cr2 register.
> >> 
> >> IMO that's best.
> > 
> > OK, I can whip up a patch, but I wont push that in till 3.6.
> > 
> 
> Thanks.  Something I've noticed is that writing cr2 is slow, so you may
> want to write it only if it has changed (which should be very rare).
> 

Is reading it fast? Then we could do a two reads and only write when
needed.

Something like this pseudo assembly
 
	mov cr2, rax
	push rax

	call do_nmi

	pop rax
	mov cr2, rbx
	cmp rax, rbx
	be skip
	mov rax, cr2
skip:


-- Steve



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