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Date: Wed, 25 Mar 2015 18:11:13 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
        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
Message-ID: <20150325171113.GA29045@redhat.com>
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> <5512C61E.3080308@intel.com>
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Hi Dave,

On 03/25, Dave Hansen wrote:
>
> 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.

Yes, iirc we alredy discussed these fixes ?

I still think that the "if (!xstate)" check at the start of
tsk_get_xsave_field() will look better, but this is cosmetic.

> 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?

I think yes. But let me remind just in case that this depends on
"x86, fpu: unlazy_fpu: don't do __thread_fpu_end() if use_eager_fpu()".

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

Oh, don't ask me ;) To me it looks fine.

Oleg.