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Date: Sat, 01 Feb 2014 15:40:13 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: George Spelvin <linux@horizon.com>, torvalds@linux-foundation.org
CC: jack@suse.cz, linux-kernel@vger.kernel.org, maarten-baert@hotmail.com,
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        sbsiddha@gmail.com, stable@vger.kernel.org, tglx@linutronix.de,
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Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt
 flag
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On 02/01/2014 01:17 PM, George Spelvin 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.
> 
> This definitely seems much more sensible.  For processors without
> optimized context save/restore, the decision whether to restore eagerly
> is best made once the kernel has decided what it's returning *to*.
> 
> From an interrupt handler, there are now three cases:
> 1) FPU not in use, available for immediate use.
> 2) FPU in use by user-space; save to <location> before using.
> 3) FPU in use by kernel code; may not be used (unless we want
>    to add nested FPU state save hair).
> 

OK, let's circle back for a bit.  We have an active bug, and we clearly
have a lot of restructuring that could/should be done.  We need to fix
the bug first; if we're going to a bunch of restructuring then that
ought to be separate.  The first bit is how we fix the immediate bug.

	-hpa

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