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

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Message-ID: <52ED562B.60703@zytor.com>
Date:	Sat, 01 Feb 2014 12:16:43 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Suresh Siddha <sbsiddha@...il.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 02/01/2014 11:46 AM, Linus Torvalds wrote:
> 
> .. which *does* actually bring up something that might work, and might
> be a good idea: remove the "restore math state or set TS" from the
> normal kernel paths *entirely*, and move it to the "return to user
> space" phase.
> 

The task switch code would have to be aware in case of preemption,
though.  The nice thing about *that* is that we could probably
completely drop the notion that we can't preempt an FPU-using kernel task.

	-hpa

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