linux-kernel - Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

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Message-ID: <CALCETrVTTh9yuXH0hfcOpytyBd25K6thPfqqUBQtnOqx90ZRqw@mail.gmail.com>
Date:	Thu, 26 Jun 2014 15:19:26 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	"Ren, Qiaowei" <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

On Wed, Jun 25, 2014 at 2:45 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 06/25/2014 02:05 PM, Andy Lutomirski wrote:
>> Hmm.  the memfd_create thing may be able to do this for you.  If you
>> created a per-mm memfd and mapped it, it all just might work.
>
> memfd_create() seems to bring a fair amount of baggage along (the fd
> part :) if all we want is a marker.  Really, all we need is _a_ bit, and
> some way to plumb to userspace the RSS values of VMAs with that bit set.
>
> Creating and mmap()'ing a fd seems a rather roundabout way to get there.

Hmm.  So does VM_MPX, though.  If this stuff were done entirely in
userspace, then memfd_create would be exactly the right solution, I
think.

Would it work to just scan the bound directory to figure out how many
bound tables exist?

--Andy
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