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From: Michal Hocko <mhocko@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Joel Stanley <joel@jms.id.au>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	"James E.J. Bottomley" <jejb@parisc-linux.org>,
	Helge Deller <deller@gmx.de>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	"David S. Miller" <davem@davemloft.net>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-mips@linux-mips.org
Subject: Re: linux-next: Tree for Nov 7
Date: Mon, 13 Nov 2017 13:00:57 +0100
Message-ID: <20171113120057.555mvrs4fjq5tyng@dhcp22.suse.cz> (raw)
In-Reply-To: <87lgjawgx1.fsf@concordia.ellerman.id.au>

On Mon 13-11-17 22:34:50, Michael Ellerman wrote:
> Hi Michal,
> 
> Michal Hocko <mhocko@kernel.org> writes:
> > On Mon 13-11-17 10:20:06, Michal Hocko wrote:
> >> [Cc arm and ppc maintainers]
> >
> > Hmm, it turned out to be a problem on other architectures as well.
> > CCing more maintainers. For your reference, we are talking about
> > http://lkml.kernel.org/r/20171023082608.6167-1-mhocko@kernel.org
> > which has broken architectures which do apply aligning on the mmap
> > address hint without MAP_FIXED applied. See below my proposed way
> > around this issue because I belive that the above patch is quite
> > valuable on its own to be dropped for all archs.
> 
> I don't really like your solution sorry :)  The fact that you've had to
> patch seven arches seems like a red flag.
> 
> I think this is a generic problem with MAP_FIXED, which I've heard
> userspace folks complain about in the past.

The thing is that we canno  change MAP_FIXED behavior as it is carved in
stone

> Currently MAP_FIXED does two things:
>   1. makes addr not a hint but the required address
>   2. blasts any existing mapping
> 
> You want 1) but not 2).

+ fail if there is a clashing range

> So the right solution IMHO would be to add a new mmap flag to request
> that behaviour, ie. a fixed address but iff there is nothing already
> mapped there.
> 
> I don't know the mm code well enough to know if that's hard for some
> reason, but it *seems* like it should be doable.

Yes, I have mentioned that in the previous email but the amount of code
would be even larger. Basically every arch which reimplements
arch_get_unmapped_area would have to special case new MAP_FIXED flag to
do vma lookup. So this was the most simple solution I could come up
with. If there was a general interest for MAP_FIXED_SAFE then we can
introduce it later of course. I would just like the hardening merged
sooner rather than later.
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07  5:22 Stephen Rothwell
2017-11-07 22:22 ` Joel Stanley
2017-11-08 14:20   ` Michal Hocko
2017-11-10 12:30     ` Michal Hocko
2017-11-12  1:08       ` Joel Stanley
2017-11-13  9:20         ` Michal Hocko
2017-11-13  9:34           ` Russell King - ARM Linux
2017-11-13  9:42           ` Michal Hocko
2017-11-13 11:34             ` Michael Ellerman
2017-11-13 12:00               ` Michal Hocko [this message]
2017-11-13 15:16                 ` Michal Hocko
2017-11-13 15:48                   ` Russell King - ARM Linux
2017-11-13 15:59                     ` Michal Hocko
2017-11-13 15:49                   ` Michal Hocko
2017-11-13 16:06                     ` Michal Hocko
2017-11-13 16:35                       ` Khalid Aziz
2017-11-14  7:07                         ` Michal Hocko
2017-11-14  9:18                       ` Michael Ellerman
2017-11-14  9:29                         ` Michal Hocko
2017-11-14  9:02                   ` Michael Ellerman
2017-11-14  8:54                 ` Michael Ellerman
2017-11-14  9:04                   ` Michal Hocko
2017-11-14 14:52                     ` Khalid Aziz
2017-11-13 14:11           ` Michal Hocko
2017-11-13 15:09             ` Russell King - ARM Linux
2017-11-13 15:31               ` Michal Hocko
2017-11-14  0:03         ` Andrew Morton
2017-11-14  0:36           ` Stephen Rothwell
  -- strict thread matches above, loose matches on Subject: below --
2019-11-07  8:07 Stephen Rothwell
2018-11-07  3:16 Stephen Rothwell
2013-11-07  7:31 Stephen Rothwell
2012-11-07  5:15 Stephen Rothwell

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