On Mon, 13 Mar 2017, Dmitry Safonov wrote: > On 03/13/2017 04:47 PM, Thomas Gleixner wrote: > > On Mon, 13 Mar 2017, Dmitry Safonov wrote: > > > On 03/13/2017 12:39 PM, Thomas Gleixner wrote: > > > > On Mon, 6 Mar 2017, Dmitry Safonov wrote: > > > > > > > > > Result of mmap() calls with MAP_32BIT flag at this moment depends > > > > > on thread flag TIF_ADDR32, which is set during exec() for 32-bit apps. > > > > > It's broken as the behavior of mmap() shouldn't depend on exec-ed > > > > > application's bitness. Instead, it should check the bitness of mmap() > > > > > syscall. > > > > > How it worked before: > > > > > o for 32-bit compatible binaries it is completely ignored. Which was > > > > > fine when there were one mmap_base, computed for 32-bit syscalls. > > > > > After introducing mmap_compat_base 64-bit syscalls do use computed > > > > > for 64-bit syscalls mmap_base, which means that we can allocate 64-bit > > > > > address with 64-bit syscall in application launched from 32-bit > > > > > compatible binary. And ignoring this flag is not expected behavior. > > > > > > > > Well, the real question here is, whether we should allow 32bit > > > > applications > > > > to obtain 64bit mappings at all. We can very well force 32bit > > > > applications > > > > into the 4GB address space as it was before your mmap base splitup and > > > > be > > > > done with it. > > > > > > Hmm, yes, we could restrict 32bit applications to 32bit mappings only. > > > But the approach which I tried to follow in the patches set, it was do > > > not base the logic on the bitness of launched applications > > > (native/compat) - only base on bitness of the performing syscall. > > > The idea was suggested by Andy and I made mmap() logic here independent > > > from original application's bitness. > > > > > > It also seems to me simpler: > > > if 32-bit application wants to allocate 64-bit mapping, it should > > > long-jump with 64-bit segment descriptor and do `syscall` instruction > > > for 64-bit syscall entry path. So, in my point of view after this dance > > > the application does not differ much from native 64-bit binary and can > > > have 64-bit address mapping. > > > > Works for me, but it lacks documentation ..... > > Sure, could you recommend a better place for it? > Should it be in-code comment in x86 mmap() code or Documentation/* > change or a patch to man-pages? I added a comment in the code and fixed up the changelogs. man-page needs some care as well. Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
