linux-kernel - Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

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Message-ID: <CA+55aFxzYMCXop7KSUi9EuaTF-m4qpbM4ahrELW8gKHDZVwkZA@mail.gmail.com>
Date:	Sat, 1 Feb 2014 17:51:07 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Suresh Siddha <sbsiddha@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Nate Eldredge <nate@...tsmathematics.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	stable <stable@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maarten Baert <maarten-baert@...mail.com>,
	Jan Kara <jack@...e.cz>, George Spelvin <linux@...izon.com>,
	Pekka Riikonen <priikone@....fi>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

On Sat, Feb 1, 2014 at 5:47 PM, Suresh Siddha <sbsiddha@...il.com> 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.

                Linus
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