From: "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
To: Jeremy Fitzhardinge <jeremy-TSDbQ3PG+2Y@public.gmane.org>
Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
akpm-3NddpPZAyC0@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] KVM: Avoid using vmx instruction directly
Date: Tue, 21 Nov 2006 10:35:48 -0800 [thread overview]
Message-ID: <45634704.8020407@zytor.com> (raw)
In-Reply-To: <4553BC18.6090207-TSDbQ3PG+2Y@public.gmane.org>
Jeremy Fitzhardinge wrote:
> Avi Kivity wrote:
>>> Or gcc
>>> might move the assignment of phys_addr to after the inline assembly.
>>>
>> "asm volatile" prevents that (and I'm not 100% sure it's necessary).
>
> No, it won't necessarily. "asm volatile" simply forces gcc to emit the
> assembler, even if it thinks its output doesn't get used. It makes no
> ordering guarantees with respect to other code (or even other "asm
> volatiles"). The "memory" clobbers should fix the ordering of the asms
> though.
>
I think you're wrong about that; in particular, I'm pretty sure "asm
volatiles" are ordered among themselves. What the "volatile" means is
"this has side effects you (the compiler) don't understand", and gcc
can't assume that it can reorder such side effects.
-hpa
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next prev parent reply other threads:[~2006-11-21 18:35 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-09 11:08 [PATCH] KVM: Avoid using vmx instruction directly Avi Kivity
2006-11-09 13:29 ` Arnd Bergmann
[not found] ` <200611091429.42040.arnd-r2nGTMty4D4@public.gmane.org>
2006-11-09 13:36 ` Avi Kivity
[not found] ` <45532EE3.4000104-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
2006-11-09 14:42 ` Arnd Bergmann
2006-11-09 14:52 ` [kvm-devel] " Avi Kivity
2006-11-09 16:37 ` Arnd Bergmann
2006-11-09 16:51 ` Avi Kivity
2006-11-09 23:39 ` Jeremy Fitzhardinge
2006-11-10 12:46 ` Martin Schwidefsky
[not found] ` <6e0cfd1d0611100446j77a27b29jc23f76a515451377-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2006-11-10 19:38 ` Jeremy Fitzhardinge
[not found] ` <4553BC18.6090207-TSDbQ3PG+2Y@public.gmane.org>
2006-11-21 18:35 ` H. Peter Anvin [this message]
[not found] ` <45634704.8020407-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
2006-11-21 19:41 ` Avi Kivity
2006-11-21 20:50 ` Jeremy Fitzhardinge
[not found] ` <4563667B.2060209-TSDbQ3PG+2Y@public.gmane.org>
2006-11-22 6:42 ` Avi Kivity
[not found] ` <4563F158.3060209-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
2006-11-22 9:10 ` Jeremy Fitzhardinge
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