From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: linux-next: Tree for Nov 7 Date: Mon, 13 Nov 2017 13:00:57 +0100 Message-ID: <20171113120057.555mvrs4fjq5tyng@dhcp22.suse.cz> References: <20171107162217.382cd754@canb.auug.org.au> <20171108142050.7w3yliulxjeco3b7@dhcp22.suse.cz> <20171110123054.5pnefm3mczsfv7bz@dhcp22.suse.cz> <20171113092006.cjw2njjukt6limvb@dhcp22.suse.cz> <20171113094203.aofz2e7kueitk55y@dhcp22.suse.cz> <87lgjawgx1.fsf@concordia.ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <87lgjawgx1.fsf@concordia.ellerman.id.au> Sender: linux-kernel-owner@vger.kernel.org To: Michael Ellerman Cc: Joel Stanley , Stephen Rothwell , Andrew Morton , Linux-Next Mailing List , Linux Kernel Mailing List , Russell King , Benjamin Herrenschmidt , Abdul Haleem , Ralf Baechle , "James E.J. Bottomley" , Helge Deller , Yoshinori Sato , Rich Felker , "David S. Miller" , Chris Zankel , Max Filippov , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-mips@linux-mips.org List-Id: linux-next.vger.kernel.org On Mon 13-11-17 22:34:50, Michael Ellerman wrote: > Hi Michal, > > Michal Hocko 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