Re: [PATCH 0/6] x86: 32-bit compatible C/R on x86_64

[Dmitry Safonov]

On 06/01/2016 04:11 PM, Dmitry Safonov wrote:
> This patches set is an attempt to add checkpoint/restore
> for 32-bit tasks in compatibility mode on x86_64 hosts.
>
> Restore in CRIU starts from one root restoring process, which
> reads info for all threads being restored from images files.
> This information is used further to to find out which processes
> share some resources. Later shared resources are restored only
> by one process and all other inherit them.
> After that it calls clone() and new threads restore their
> properties in parallel. Those threads inherit all parent's
> mappings and fetch properties from those mappings
> (and do clone themself, if they have children/subthreads). [1]
> Then starts restorer blob's play, it's PIE binary, which
> unmaps all unneeded for restoring VMAs, maps new VMAs and
> finalize restoring with sigreturn syscall. [2]
>
> To restore of 32-bit task we need three things to do in running
> x86_64 restorer blob:
> a) set code selector to __USER32_CS (to run 32-bit code);
> b) remap vdso blob from 64-bit to 32-bit
>    This is primary needed because restore may happen on a different
>    kernel, which has different vDSO image than we had on dump.
> c) if 32-bit vDSO differ to dumped image, move it on free place
>    and add jump trampolines to that place.
> d) switch TIF_IA32 flag, so kernel would know that it deals with
>    compatible 32-bit application.
>
> From all this:
> a) setting CS may be done from userspace, no patches needed;
> b) patches 1-3 add ability to map different vDSO blobs on x86 kernel;
> c) for remapping/moving 32-bit vDSO blob patches have been send earlier
>    and seems to be accepted [3]
> d) and for swapping TIF_IA32 flag discussion with Andy ended in conclusion
>    that it's better to remove this flag completely.
>    Patches 4-6 deletes usage of TIF_IA32 from ptrace, signal and coredump
>    code. This is rework/resend of RFC [4]
>
> [1] https://criu.org/Checkpoint/Restore#Restore
> [2] https://criu.org/Restorer_context
> [3] https://lkml.org/lkml/2016/5/17/243
> [4] https://lkml.org/lkml/2016/4/25/650
>
> Dmitry Safonov (6):
>   x86/vdso: unmap vdso blob on vvar mapping failure
>   x86/vdso: introduce do_map_vdso() and vdso_type enum
>   x86/arch_prctl/vdso: add ARCH_MAP_VDSO_*
>   x86/coredump: use core regs, rather that TIF_IA32 flag
>   x86/ptrace: down with test_thread_flag(TIF_IA32)
>   x86/signal: add SA_{X32,IA32}_ABI sa_flags

Oh, forgot to mention: this patches set is based on [3],
so kernel build bot may be not happy about applying them.
Anyway, I hope for the next revisions, the base-patches
will be applied to linux-next and build-bot will test them
just fine.

>  arch/x86/entry/vdso/vma.c          | 72 +++++++++++++++++++++-----------------
>  arch/x86/ia32/ia32_signal.c        |  2 +-
>  arch/x86/include/asm/compat.h      |  8 ++---
>  arch/x86/include/asm/fpu/signal.h  |  6 ++++
>  arch/x86/include/asm/vdso.h        |  4 +++
>  arch/x86/include/uapi/asm/prctl.h  |  6 ++++
>  arch/x86/include/uapi/asm/signal.h |  6 +++-
>  arch/x86/kernel/process_64.c       | 10 ++++++
>  arch/x86/kernel/ptrace.c           |  2 +-
>  arch/x86/kernel/signal.c           | 19 +++++-----
>  arch/x86/kernel/signal_compat.c    | 30 ++++++++++++++--
>  fs/binfmt_elf.c                    | 18 +++++-----
>  kernel/signal.c                    |  5 +++
>  13 files changed, 129 insertions(+), 59 deletions(-)


--
Regards,
Dmitry Safonov