Run armv7 32 bit userspace on aarch64

[Will Deacon]

On Mon, Oct 12, 2015 at 10:38:25AM -0700, Shi, Yang wrote:
> BTW, it may be related to unaligned address.
> 
> init[1]: unhandled level 3 translation fault (11) at 0x43acfad3, esr
> 0x92000047
> pgd = ffff80007b8be000
> [43acfad3] *pgd=00000000fb8c5003, *pud=00000000fb8c1003,
> *pmd=00000000fb8c2003, *pte=0000000000000000
> 
> The userspace is trying to write to 0x43acfad3, the permission is
> readonly.

What's the instruction making the access? If it's a store-multiple, then
we don't support that in the arm64 kernel. It would be nice if the 32-bit
kernel had the same behaviour, but the patch seems to have stalled and
probably doesn't apply anymore:

  http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=7944/1

Will