On Wed, May 14, 2014 at 3:11 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > On Wed, May 14, 2014 at 02:33:54PM -0700, Andy Lutomirski wrote: >> On Wed, May 14, 2014 at 2:31 PM, Andrew Morton >> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >> > On Wed, 14 May 2014 17:11:00 -0400 Sasha Levin <sasha.levin@xxxxxxxxxx> wrote: >> > >> >> > In my linux-next all that code got deleted by Andy's "x86, vdso: >> >> > Reimplement vdso.so preparation in build-time C" anyway. What kernel >> >> > were you looking at? >> >> >> >> Deleted? It appears in today's -next. arch/x86/vdso/vma.c:124 . >> >> >> >> I don't see Andy's patch removing that code either. >> > >> > ah, OK, it got moved from arch/x86/vdso/vdso32-setup.c into >> > arch/x86/vdso/vma.c. >> > >> > Maybe you managed to take a fault against the symbol area between the >> > _install_special_mapping() and the remap_pfn_range() call, but mmap_sem >> > should prevent that. >> > >> > Or the remap_pfn_range() call never happened. Should map_vdso() be >> > running _install_special_mapping() at all if >> > image->sym_vvar_page==NULL? >> >> I'm confused: are we talking about 3.15-rcsomething or linux-next? >> That code changed. >> >> Would this all make more sense if there were just a single vma in >> here? cc: Pavel and Cyrill, who might have to deal with this stuff in >> CRIU > > Well, for criu we've not modified any vdso kernel's code (except > setting VM_SOFTDIRTY for this vdso VMA in _install_special_mapping). > And never experienced problems Sasha points. Looks like indeed in > -next code is pretty different from mainline one. To figure out > why I need to fetch -next branch and get some research. I would > try to do that tomorrow (still hoping someone more experienced > in mm system would beat me on that). I can summarize: On 3.14 and before, the vdso is just a bunch of ELF headers and executable data. When executed by 64-bit binaries, it reads from the fixmap to do its thing. That is, it reads from kernel addresses that don't have vmas. When executed by 32-bit binaries, it doesn't read anything, since there was no 32-bit timing code. On 3.15, the x86_64 vdso is unchanged. The 32-bit vdso is preceded by a separate vma containing two pages worth of time-varying read-only data. The vdso reads those pages using PIC references. On linux-next, all vdsos work the same way. There are two vmas. The first vma is executable text, which can be poked at by ptrace, etc normally. The second vma contains time-varying state, should not allow poking, and is accessed by PIC references. What does CRIU do to restore the vdso? Will 3.15 and/or linux-next need to make some concession for CRIU? --Andy -- 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>