RFC uprobes: kill xol vma

Hello.

On top of this series, not for inclusion yet, just to explain what I mean. May be someone can test it ;)

This series kills xol_vma. Instead we use the per_cpu-like xol slots.

This is much more simple and efficient. And this of course solves many problems we currently have with xol_vma.

For example, we simply can not trust it. We do not know what actually we are going to execute in UTASK_SSTEP mode. An application can unmap this area and then do mmap(PROT_EXEC|PROT_WRITE, MAP_FIXED) to fool uprobes.

The only disadvantage is that this adds a bit more arch-dependant code.

The main question, can this work? I know very little in this area. And I am not sure if this can be ported to other architectures.

Please comment.

Oleg.

 arch/x86/include/asm/fixmap.h      |    9 +
 arch/x86/include/asm/thread_info.h |    4 
 arch/x86/kernel/process.c          |    6 
 arch/x86/kernel/uprobes.c          |   26 +++-
 include/linux/mm_types.h           |    1 
 include/linux/uprobes.h            |   27 ----
 kernel/fork.c                      |    2 
 kernel/uprobes.c                   |  239 +++----------------------------------
 8 files changed, 71 insertions(+), 243 deletions(-)

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