From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Martin Schwidefsky <schwidefsky@googlemail.com>
Cc: Avi Kivity <avi@qumranet.com>, Arnd Bergmann <arnd@arndb.de>,
kvm-devel@lists.sourceforge.net, akpm@osdl.org,
linux-kernel@vger.kernel.org
Subject: Re: [kvm-devel] [PATCH] KVM: Avoid using vmx instruction directly
Date: Fri, 10 Nov 2006 11:38:32 -0800 [thread overview]
Message-ID: <4554D538.10404@goop.org> (raw)
In-Reply-To: <6e0cfd1d0611100446j77a27b29jc23f76a515451377@mail.gmail.com>
Martin Schwidefsky wrote:
> On 11/10/06, Jeremy Fitzhardinge <jeremy@goop.org> 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.
>
> The "memory" clobber just tells the compiler that any memory object
> might get access by the inline.
I just meant that two asms with a "memory" clobber will be generated
with a fixed ordering, which "asm volatile" does not necessarily do.
J
WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Fitzhardinge <jeremy-TSDbQ3PG+2Y@public.gmane.org>
To: Martin Schwidefsky <schwidefsky-gM/Ye1E23mwN+BqQ9rBEUg@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: Fri, 10 Nov 2006 11:38:32 -0800 [thread overview]
Message-ID: <4554D538.10404@goop.org> (raw)
In-Reply-To: <6e0cfd1d0611100446j77a27b29jc23f76a515451377-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
Martin Schwidefsky wrote:
> On 11/10/06, Jeremy Fitzhardinge <jeremy-TSDbQ3PG+2Y@public.gmane.org> 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.
>
> The "memory" clobber just tells the compiler that any memory object
> might get access by the inline.
I just meant that two asms with a "memory" clobber will be generated
with a fixed ordering, which "asm volatile" does not necessarily do.
J
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next prev parent reply other threads:[~2006-11-10 19:39 UTC|newest]
Thread overview: 25+ 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 11:08 ` Avi Kivity
2006-11-09 13:29 ` [kvm-devel] " Arnd Bergmann
2006-11-09 13:29 ` Arnd Bergmann
2006-11-09 13:36 ` [kvm-devel] " Avi Kivity
2006-11-09 13:36 ` Avi Kivity
2006-11-09 14:42 ` [kvm-devel] " Arnd Bergmann
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
2006-11-10 19:38 ` Jeremy Fitzhardinge [this message]
2006-11-10 19:38 ` Jeremy Fitzhardinge
2006-11-21 18:35 ` [kvm-devel] " H. Peter Anvin
2006-11-21 18:35 ` H. Peter Anvin
2006-11-21 19:41 ` [kvm-devel] " Avi Kivity
2006-11-21 19:41 ` Avi Kivity
2006-11-21 20:50 ` [kvm-devel] " Jeremy Fitzhardinge
2006-11-21 20:50 ` Jeremy Fitzhardinge
2006-11-22 6:42 ` [kvm-devel] " Avi Kivity
2006-11-22 6:42 ` Avi Kivity
2006-11-22 9:10 ` [kvm-devel] " Jeremy Fitzhardinge
2006-11-22 9:10 ` Jeremy Fitzhardinge
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