linux-kernel - Re: [PATCH 01/17] x86, fpu: wrap get_xsave

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Date:	Wed, 25 Mar 2015 07:28:46 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer

On 03/25/2015 05:45 AM, Oleg Nesterov wrote:
> So far I do not understand this discussion ;) I didn't see the patches
> and other emails...

Hi Oleg,

My patch set apparently didn't make it to LKML, but here are the two
relevant ones.  We're essentially replacing the MPX use of
fpu_save_init().  CPUs with MPX should entirely have eager FPU mode on.
 But, the edges of the MPX code (do_bounds()) will call this to
distinguish a plain #BR exception from a #BR caused by MPX.  It may get
called on CPUs without eager FPU mode on.

> http://git.kernel.org/cgit/linux/kernel/git/daveh/x86-mpx.git/commit/?h=mpx-v16&id=92d3e7c1664f766142904904e27e126888adb8a7
> http://git.kernel.org/cgit/linux/kernel/git/daveh/x86-mpx.git/commit/?h=mpx-v16&id=18049953ae43a7ffa084a01613c1684bdf24dd2e

All that the MPX code wants here is to read the in-memory copy of the
MPX registers, or error out.

So, for the purposes of this series:

With the (so far unmerged to Linus's tree) changes to unlazy_fpu(), does
tsk_get_xsave_field()'s use of unlazy_fpu() look correct?

Should we also be renaming tsk_get_xsave_field() to something more
appropriate?
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