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Date:	Sat, 01 Feb 2014 17:57:30 -0800
From:	"H. Peter Anvin" <>
To:	Linus Torvalds <>,
	Suresh Siddha <>
CC:	Nate Eldredge <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,
	the arch/x86 maintainers <>,
	stable <>,
	Linux Kernel Mailing List <>,
	Maarten Baert <>,
	Jan Kara <>, George Spelvin <>,
	Pekka Riikonen <>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt

On 02/01/2014 05:51 PM, Linus Torvalds wrote:
> On Sat, Feb 1, 2014 at 5:47 PM, Suresh Siddha <> wrote:
>> So if the restore failed, we should do something like drop_init_fpu(),
>> which will restore init-state to the registers.
>> for eager-fpu()  paths we don't use clts() stts() etc.
> Uhhuh. Ok.
> Why do we do that, btw? I think it would make much more sense to just
> do what I *thought* we did, and just make it a context-switch-time
> optimization ("let's always switch FP state"), not make it a huge
> semantic difference.

Twiddling CR0.TS is pretty slow if we're not taking advantage of it.


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