Re: [PATCH] KVM: Avoid using vmx instruction directly

Avi Kivity
2006-11-22T06:42:32Z

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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