Re: [PATCH v2 00/19] Add generic vdso_base tracking

Christophe Leroy
2020-11-24T06:54:04Z

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-dima@arista.com/
>
> [1]: https://lore.kernel.org/linux-arch/CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com/
> [2]: https://github.com/checkpoint-restore/criu/issues/488
>

Christophe