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Date: Wed, 25 Mar 2015 07:28:46 -0700
From: Dave Hansen <dave.hansen@intel.com>
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To: Oleg Nesterov <oleg@redhat.com>, Andy Lutomirski <luto@amacapital.net>
CC: Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>,
        Rik van Riel <riel@redhat.com>, Suresh Siddha <sbsiddha@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Fenghua Yu <fenghua.yu@intel.com>
Subject: Re: [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer
References: <1427235664-25318-1-git-send-email-dave.hansen@intel.com> <1427235664-25318-2-git-send-email-dave.hansen@intel.com> <CALCETrV864te0pYhKewGzZGvfEJYkYs1kCTjHW8HkncrugYChw@mail.gmail.com> <5511F65A.5020505@intel.com> <CALCETrUxfd8brhWzBJSsSA=M1OHOSUWtu73gosPGZV9QgM6Z4Q@mail.gmail.com> <5511FD59.3040503@intel.com> <CALCETrVmxg3qKJ4=3karW69PTy=Ascg_sZmsm=WtF9AO+JB-+w@mail.gmail.com> <20150325124533.GA17191@redhat.com>
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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?