From: Avi Kivity <avi@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
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 17:37:22 +0300 [thread overview]
Message-ID: <4FBBA4A2.2070501@redhat.com> (raw)
In-Reply-To: <1337696825.13348.44.camel@gandalf.stny.rr.com>
On 05/22/2012 05:27 PM, Steven Rostedt wrote:
> 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.
The upside is 70 cycles on one machine, see d3edefc0035669.
>
> 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.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2012-05-22 14:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-22 12:53 NMI vs #PF clash 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 [this message]
2012-05-22 14:50 ` Steven Rostedt
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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