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

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Date:	Thu, 29 Jan 2015 20:33:38 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Dave Hansen <dave.hansen@...ux.intel.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

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On 01/29/2015 06:26 PM, Dave Hansen wrote:
> On 01/29/2015 01:56 PM, Oleg Nesterov wrote:
>> --- x/arch/x86/kernel/traps.c +++ x/arch/x86/kernel/traps.c @@
>> -313,7 +313,7 @@ dotraplinkage void do_bounds(struct pt_r * It is
>> not directly accessible, though, so we need to * do an xsave and
>> then pull it out of the xsave buffer. */ -
>> fpu_save_init(&tsk->thread.fpu); +	unlazy_fpu(tsk); xsave_buf =
>> &(tsk->thread.fpu.state->xsave);
> ...
>> bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);
> 
> 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.

- -- 
All rights reversed
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