From: Michal Hocko <mhocko@kernel.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
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>,
linux-arm-kernel@lists.infradead.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: linux-next: Tree for Nov 7
Date: Mon, 13 Nov 2017 16:31:42 +0100 [thread overview]
Message-ID: <20171113153142.aoznpjivgjjihlef@dhcp22.suse.cz> (raw)
In-Reply-To: <20171113150908.GL12318@n2100.armlinux.org.uk>
On Mon 13-11-17 15:09:09, Russell King - ARM Linux wrote:
> On Mon, Nov 13, 2017 at 03:11:40PM +0100, Michal Hocko wrote:
> > On Mon 13-11-17 10:20:06, Michal Hocko wrote:
> > > [Cc arm and ppc maintainers]
> > >
> > > Thanks a lot for testing!
> > >
> > > On Sun 12-11-17 11:38:02, Joel Stanley wrote:
> > > > On Fri, Nov 10, 2017 at 11:00 PM, Michal Hocko <mhocko@kernel.org> wrote:
> > > > > Hi Joel,
> > > > >
> > > > > On Wed 08-11-17 15:20:50, Michal Hocko wrote:
> > > > > [...]
> > > > >> > There are a lot of messages on the way up that look like this:
> > > > >> >
> > > > >> > [ 2.527460] Uhuuh, elf segement at 000d9000 requested but the
> > > > >> > memory is mapped already
> > > > >> > [ 2.540160] Uhuuh, elf segement at 000d9000 requested but the
> > > > >> > memory is mapped already
> > > > >> > [ 2.546153] Uhuuh, elf segement at 000d9000 requested but the
> > > > >> > memory is mapped already
> > > > >> >
> > > > >> > And then trying to run userspace looks like this:
> > > > >>
> > > > >> Could you please run with debugging patch posted
> > > > >> http://lkml.kernel.org/r/20171107102854.vylrtaodla63kc57@dhcp22.suse.cz
> > > > >
> > > > > Did you have chance to test with this debugging patch, please?
> > > >
> > > > Lots of this:
> > > >
> > > > [ 1.177266] Uhuuh, elf segement at 000d9000 requested but the memory is mapped already, got 000dd000
> > > > [ 1.177555] Clashing vma [dd000, de000] flags:100873 name:(null)
> > >
> > > This smells like the problem I've expected that mmap with hint doesn't
> > > respect the hint even though there is no clashing mapping. The above
> > > basically says that we didn't map at 0xd9000 but it has placed it at
> > > 0xdd000. The nearest (clashing) vma is at 0xdd000 so this is our new
> > > mapping. find_vma returns the closest vma (with addr < vm_end) for the
> > > given address 0xd9000 so this address cannot be mapped by any other vma.
> > >
> > > Now that I am looking at arm's arch_get_unmapped_area it does perform
> > > aligning for shared vmas.
> >
> > Sorry for confusion here. These are not shared mappings as pointed out
> > by Russell in a private email. I got confused by the above flags which I
> > have misinterpreted as bit 0 set => MAP_SHARED. These are vm_flags
> > obviously so the bit 0 is VM_READ. Sorry about the confusion. The real
> > reason we are doing the alignment is that we do a file mapping
> > /*
> > * We only need to do colour alignment if either the I or D
> > * caches alias.
> > */
> > if (aliasing)
> > do_align = filp || (flags & MAP_SHARED);
> >
> > I am not really familiar with this architecture to understand why do we
> > need aliasing for file mappings, though.
>
> I think it's there so that flush_dcache_page() works - possibly
> get_user_pages() being used on a private mapping of page cache pages,
> but that's guessing.
I fail to see how the mixure of MAP_FIXED and regular mapping of the
same file work then, but as I've said I really do not understand this
code.
> I'm afraid I don't remember all the details, this is code from around
> 15 years ago, and I'd be very nervous about changing it now without
> fully understanding the issues.
Ohh, absolutely! I didn't dare to touch this code and that's why I took
the easy way and simply opt-out from the harding for all those archs
that are basically sharing this pattern. But after a closer look it
seems that we can really introduce MAP_FIXED_SAFE that would keep the
arch mmap code intact yet we would get the hardening for all archs.
It would allow also allow a safer MAP_FIXED semantic for userspace.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-11-13 15:31 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-07 5:22 linux-next: Tree for Nov 7 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
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 [this message]
2017-11-14 0:03 ` Andrew Morton
2017-11-14 0:36 ` Stephen Rothwell
-- strict thread matches above, loose matches on Subject: below --
2023-11-07 1:17 Stephen Rothwell
2022-11-07 3:44 Stephen Rothwell
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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