linux-kernel - Re: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API to arch

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Date:	Tue, 6 Jan 2015 22:39:00 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	ilya.enkovich@...el.com
Subject: Re: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API
 to arch_prctl

On Tue, Jan 06, 2015 at 01:34:56PM -0800, Andy Lutomirski wrote:
> On Tue, Jan 6, 2015 at 1:22 PM, Andi Kleen <andi@...stfloor.org> wrote:
> >> Given that it doesn't seen to have been committed yet, I'm not too
> >> worried about compatibility.  And "prctl (43)" doesn't actually seem a
> >> whole lot better than "syscall(SYS_arch_prctl, ARCH_ENABLE_MPX, 0)"
> >
> > This would actually fail with the EINVAL change you requested.
> >
> 
> So the libmpx code needs to change anyway, then, right?  I really
> don't think we should accept garbage in the extra prctl slots just
> because uncommitted code somewhere fails to initialize them.

Yes it would.

I think that is why most prctls don't do it. After all if you need a new
field you can just add another one. I usually added the checks in the
ones I added, but I can see why not doing it.

-Andi
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