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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>
Subject: Re: NMI vs #PF clash
Date: Tue, 22 May 2012 10:50:29 -0400	[thread overview]
Message-ID: <1337698229.13348.46.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <4FBBA4A2.2070501@redhat.com>

On Tue, 2012-05-22 at 17:37 +0300, Avi Kivity wrote:
> > 
> > 
> > Is reading it fast? Then we could do a two reads and only write when
> > needed.
> 
> The upside is 70 cycles on one machine, see d3edefc0035669.

Thanks

> 
> 
> > 
> > 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:
> > 
> 
> 
> Yes, provided no exceptions can happen at those points.

Yes, exceptions can only happen in the do_nmi area. There should not be
any breakpoints or page faults in the assembly code of the NMI handler.

Now another NMI may come in at any point here, but it will detect that
it is nested and return without doing anything (but telling this NMI to
repeat itself).

-- Steve



  reply	other threads:[~2012-05-22 14:50 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-05-22 12:53 Avi Kivity
2012-05-22 13:30 ` Steven Rostedt
2012-05-22 13:45   ` Avi Kivity
2012-05-22 14:09     ` Steven Rostedt
2012-05-22 14:20       ` Avi Kivity
2012-05-22 14:27         ` Steven Rostedt
2012-05-22 14:37           ` Avi Kivity
2012-05-22 14:50             ` Steven Rostedt [this message]
2012-05-22 15:22               ` Mathieu Desnoyers
2012-05-22 15:33           ` Linus Torvalds
2012-05-22 15:45             ` Avi Kivity
2012-05-22 15:47             ` H. Peter Anvin
2012-05-23  0:39             ` Steven Rostedt
2012-05-23  1:26               ` Brian Gerst
2012-05-23  8:32                 ` Steven Rostedt
2012-05-23  8:56                 ` Steven Rostedt
2012-06-11  4:22                   ` [tip:x86/debug] x86: Save cr2 in NMI in case NMIs take a page fault tip-bot for Steven Rostedt
2012-06-11  4:24 ` [tip:x86/debug] x86: Save cr2 in NMI in case NMIs take a page fault (for i386) tip-bot for Steven Rostedt

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