On Mon, Mar 13, 2017 at 6:47 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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. I agree. > > Works for me, but it lacks documentation ..... > > Thanks, > > tglx -- Andy Lutomirski AMA Capital Management, LLC -- 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>
