Re: [PATCH] x86, fpu: avoid FPU lazy restore after suspend

[H. Peter Anvin]

On 11/30/2012 11:25 AM, Linus Torvalds wrote:
> 
> and in fact I think the right place to do this *might* be in
> "native_cpu_die()" instead, at which point it would actually be
> something like
> 
>     per_cpu(fpu_owner_task, cpu) = NULL;
> 
> *after* the CPU is dead, so that nothing ever can actually see the
> state where a process is still running on the CPU and might possibly
> use the FPU.
> 
> I dunno. I think doing it after really killing the CPU (ie in the
> native_cpu_die() function) might be easier to think about, but I don't
> really hate your patch either (it does make me go "ok, we need to
> guarantee no scheduling or FP use after" - which is probably true, but
> it's still some non-local thing). Either way, a comment about it and
> abstracting whatever the invalidation sequence is in fpu-internal.h
> sounds like a good idea.
> 

Hmm... from my point of view it would almost seem saner to do this on
the way *up*... as part of CPU (re-)initialization.  After all, the
"nothing is currently running on this CPU" is part of the initial state
of the CPU, regardless of if we have ever been online before or not.

	-hpa

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