linux-kernel - [PATCH 0/6] x86: 32-bit compatible C/R on x86

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Date:	Wed, 1 Jun 2016 16:11:31 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	<linux-kernel@...r.kernel.org>, <mingo@...hat.com>
CC:	<luto@...capital.net>, <tglx@...utronix.de>, <hpa@...or.com>,
	<x86@...nel.org>, <0x7f454c46@...il.com>, <oleg@...hat.com>,
	<gorcunov@...nvz.org>, <xemul@...tuozzo.com>,
	<khorenko@...tuozzo.com>, Dmitry Safonov <dsafonov@...tuozzo.com>
Subject: [PATCH 0/6] x86: 32-bit compatible C/R on x86_64

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

 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(-)

-- 
2.8.2