Message-ID: <4563F158.3060209@qumranet.com>
Date: Wed, 22 Nov 2006 08:42:32 +0200
From: Avi Kivity <avi@qumranet.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: "H. Peter Anvin" <hpa@zytor.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
References: <4563667B.2060209@goop.org>
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Jeremy Fitzhardinge wrote:
>
>
> Like "volatile" variables, I think "asm volatile" is probably overused.
> If you want to guarantee specific ordering of asms, it's probably better
> to add an explicit dependency between them rather than rely on asm
> volatile; this could either be a "memory" clobber, or something more
> fine-grained.  For example:
>
>     /* need never be instansiated; never actually referenced */
>     extern int spin_sequencer;
>
>     /* %0 never referenced */
>     asm("take spinlock" : "+m" (spin_sequencer)...);
>
>     ...
>
>     /* again, %0 never referenced */
>     asm("release spinlock" : "+m" (spin_sequencer)...);
>

Very interesting.

Will it work on load/store architectures?  Since all memory access is 
through a register, won't the constraint generate a useless register 
load (and a use of the variable)?


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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