linux-kernel - Re: [PATCH 0/3]: x86, fpu: unlazy

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Date:	Mon, 02 Feb 2015 10:11:23 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Rik van Riel <riel@...hat.com>, Oleg Nesterov <oleg@...hat.com>
CC:	Suresh Siddha <sbsiddha@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3]: x86, fpu: unlazy_fpu fixes/cleanups

On 01/29/2015 05:33 PM, Rik van Riel wrote:
>> > Hmm, if the the thread was not using the FPU, and this fails to
>> > save anything in to the xsave_buf, what will bndcsr point to?
> If the thread was not using the FPU, can we reach the
> bound range exception?
> 
> I believe the MPX feature uses information in the xstate.

There are really two kinds of bounds exceptions.  There is an "old"
'BOUND' instruction that will generate #BR's as well as the new MPX
instructions.  The new ones require xstate and poking the FPU, etc...
The old one did not.

So, we _can_ as far as I know get in to do_bounds() without using the FPU.
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