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SubjectRe: [PATCH] Make math_state_restore() save and restore the interrupt flag
On 02/01/2014 11:27 AM, Linus Torvalds wrote:
>
> (a) "we don't want to restore at all, because once the kernel starts
> using math, it might do so a lot, and saving/restoring is a bad idea":
>
> void __kernel_fpu_end(void)
> {
> stts();
> }
>
> *or*
>
> Quite frankly, I'd almost lean towards (a). Comments? Does anybody
> have any loads where the kernel does a lot of fpu stuff (ie network
> encryption using the hw engines or something)? I'd really like to hear
> if it makes a difference..
>

This will obviously not protect eageronly features (MPX, LWP, ...) so
this means those features are permanently unavailable to the kernel,
even inside kernel_fpu_begin/end. Now, currently I don't think we have
any plans to use those in the kernel (at least not in a way where
kernel_fpu_begin/end makes sense as bracketing), but it is something
worth keeping in mind.

-hpa



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