Le 24/11/2020 à 01:29, Dmitry Safonov a écrit :
v2 Changes:
- Rename user_landing to vdso_base as it tracks vDSO VMA start address,
rather than the explicit address to land (Andy)
- Reword and don't use "new-execed" and "new-born" task (Andy)
- Fix failures reported by build robot
Started from discussion [1], where was noted that currently a couple of
architectures support mremap() for vdso/sigpage, but not munmap().
If an application maps something on the ex-place of vdso/sigpage,
later after processing signal it will land there (good luck!)
Patches set is based on linux-next (next-20201123) and it depends on
changes in x86/cleanups (those reclaim TIF_IA32/TIF_X32) and also
on my changes in akpm (fixing several mremap() issues).
I have a series that cleans up VDSO init on powerpc and migrates powerpc to
_install_special_mapping() (patch 10 of the series).
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=204396&state=%2A&archive=both
I'm wondering how we should coordinate with your series for merging.
I guess your series will also imply removal of arch_unmap() ? see
https://elixir.bootlin.com/linux/v5.10-rc4/source/arch/powerpc/include/asm/mmu_context.h#L262
Logically, the patches set divides on:
- patch 1: a cleanup for patches in x86/cleanups
- patches 2-11: cleanups for arch_setup_additional_pages()
- patches 12-13: x86 signal changes for unmapped vdso
- patches 14-19: provide generic vdso_base in mm_struct
In the end, besides cleanups, it's now more predictable what happens for
applications with unmapped vdso on architectures those support .mremap()
for vdso/sigpage.
I'm aware of only one user that unmaps vdso - Valgrind [2].
(there possibly are more, but this one is "special", it unmaps vdso, but
not vvar, which confuses CRIU [Checkpoint Restore In Userspace], that's
why I'm aware of it)
Patches as a .git branch:
https://github.com/0x7f454c46/linux/tree/setup_additional_pages-v2
v1 Link:
https://lore.kernel.org/lkml/20201108051730.2042693-1-d...@arista.com/
[1]:
https://lore.kernel.org/linux-arch/cajwjo6zanqykshbq+3b+fi_vt80mtrzev5yreqawx-l8j8x...@mail.gmail.com/
[2]: https://github.com/checkpoint-restore/criu/issues/488
Christophe