Messages in this thread | | | Subject | Re: [PATCH] powerpc/vdso: Separate vvar vma from vdso | From | Christophe Leroy <> | Date | Tue, 30 Mar 2021 10:41:18 +0200 |
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Le 26/03/2021 à 20:17, Dmitry Safonov a écrit : > Since commit 511157ab641e ("powerpc/vdso: Move vdso datapage up front") > VVAR page is in front of the VDSO area. In result it breaks CRIU > (Checkpoint Restore In Userspace) [1], where CRIU expects that "[vdso]" > from /proc/../maps points at ELF/vdso image, rather than at VVAR data page. > Laurent made a patch to keep CRIU working (by reading aux vector). > But I think it still makes sence to separate two mappings into different > VMAs. It will also make ppc64 less "special" for userspace and as > a side-bonus will make VVAR page un-writable by debugger (which previously > would COW page and can be unexpected). > > I opportunistically Cc stable on it: I understand that usually such > stuff isn't a stable material, but that will allow us in CRIU have > one workaround less that is needed just for one release (v5.11) on > one platform (ppc64), which we otherwise have to maintain. > I wouldn't go as far as to say that the commit 511157ab641e is ABI > regression as no other userspace got broken, but I'd really appreciate > if it gets backported to v5.11 after v5.12 is released, so as not > to complicate already non-simple CRIU-vdso code. Thanks! > > Cc: Andrei Vagin <avagin@gmail.com> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Cc: Christophe Leroy <christophe.leroy@csgroup.eu> > Cc: Laurent Dufour <ldufour@linux.ibm.com> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Paul Mackerras <paulus@samba.org> > Cc: linuxppc-dev@lists.ozlabs.org > Cc: stable@vger.kernel.org # v5.11 > [1]: https://github.com/checkpoint-restore/criu/issues/1417 > Signed-off-by: Dmitry Safonov <dima@arista.com> > Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu> > --- > arch/powerpc/include/asm/mmu_context.h | 2 +- > arch/powerpc/kernel/vdso.c | 54 +++++++++++++++++++------- > 2 files changed, 40 insertions(+), 16 deletions(-) >
> @@ -133,7 +135,13 @@ static int __arch_setup_additional_pages(struct linux_binprm *bprm, int uses_int > * install_special_mapping or the perf counter mmap tracking code > * will fail to recognise it as a vDSO. > */ > - mm->context.vdso = (void __user *)vdso_base + PAGE_SIZE; > + mm->context.vdso = (void __user *)vdso_base + vvar_size; > + > + vma = _install_special_mapping(mm, vdso_base, vvar_size, > + VM_READ | VM_MAYREAD | VM_IO | > + VM_DONTDUMP | VM_PFNMAP, &vvar_spec); > + if (IS_ERR(vma)) > + return PTR_ERR(vma); > > /* > * our vma flags don't have VM_WRITE so by default, the process isn't
IIUC, VM_PFNMAP is for when we have a vvar_fault handler. Allthough we will soon have one for handle TIME_NS, at the moment powerpc doesn't have that handler. Isn't it dangerous to set VM_PFNMAP then ?
Christophe
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