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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx > > > > > > > > > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
