On Wed, 4 Dec 2019, David Laight wrote:
We used to have separate get_user_unaligned() & put_user_unaligned() which would suggest that it's expected that get_user() & put_user() require their accesses be aligned, but they were removed by commit 3170d8d226c2 ("kill {__,}{get,put}_user_unaligned()") in v4.13.
But perhaps we should just take the second AdEL exception & recover via the fixups table. We definitely don't right now... Needs further investigation...
get/put_user can fault because the user page is absent (etc). So there must be code to 'expect' a fault on those instructions.
As I recall we only emulate unaligned accesses with a subset of integer load/store instructions (and then only if TIF_FIXADE is set, which is the default), and never with FP load/store instructions. Consequently I see no point in doing this in the FP emulator either and I think these ought to just send SIGBUS instead. Otherwise you'll end up with user code that works differently depending on whether the FP hardware is real or emulated, which is really bad.
FWIW,
Maciej