Comment 1 for bug 1757193

The upstream commit that fixes 706276543b69 ("x86, extable: Switch to relative exception table entries") (which the problematic commit tries to do as well) is:

ommit 548acf19234dbda5a52d5a8e7e205af46e9da840
Author: Tony Luck <email address hidden>
Date: Wed Feb 17 10:20:12 2016 -0800

    x86/mm: Expand the exception table logic to allow new handling options

    Huge amounts of help from Andy Lutomirski and Borislav Petkov to
    produce this. Andy provided the inspiration to add classes to the
    exception table with a clever bit-squeezing trick, Boris pointed
    out how much cleaner it would all be if we just had a new field.

    Linus Torvalds blessed the expansion with:

      ' I'd rather not be clever in order to save just a tiny amount of space
        in the exception table, which isn't really criticial for anybody. '

    The third field is another relative function pointer, this one to a
    handler that executes the actions.

    We start out with three handlers:

     1: Legacy - just jumps the to fixup IP
     2: Fault - provide the trap number in %ax to the fixup code
     3: Cleaned up legacy for the uaccess error hack

    Signed-off-by: Tony Luck <email address hidden>
    Reviewed-by: Borislav Petkov <email address hidden>
    Cc: Linus Torvalds <email address hidden>
    Cc: Peter Zijlstra <email address hidden>
    Cc: Thomas Gleixner <email address hidden>
    Link: http://lkml.kernel.org/r/f6af78fcbd348cf4939875cfda9c19689b5e50b8<email address hidden>
    Signed-off-by: Ingo Molnar <email address hidden>