[PATCH 1/3] arm64: armv8_deprecated: Fix swp_handler() signal generation

[Will Deacon]

On Tue, Apr 20, 2021 at 04:50:12PM +0000, Liam Howlett wrote:
> arm64_notify_segfault() was written to decide on the si_code from the
> assembly emulation of the swp_handler(), but was also used for the
> signal generation from failed access_ok() and unaligned instructions.
> 
> When access_ok() fails, there is no need to search for the offending
> address in the VMA space.  Instead, simply set the error to SIGSEGV with
> si_code SEGV_ACCERR.
> 
> Change the return code from emulate_swpX() when there is an unaligned
> pointer so the caller can differentiate from the EFAULT.  It is
> unnecessary to search the VMAs in the case of an unaligned pointer.
> This change uses SIGSEGV and SEGV_ACCERR instead of SIGBUS to keep with
> what was returned before.
> 
> Fixes: bd35a4adc413 (arm64: Port SWP/SWPB emulation support from arm)
> Signed-off-by: Liam R. Howlett <Liam.Howlett at Oracle.com>
> ---
>  arch/arm64/kernel/armv8_deprecated.c | 20 +++++++++++++-------

Can you give an example of something that is fixed by this, please? At first
glance, it doesn't look like it changes the user-visible behaviour.

We should also be compatible with arch/arm/ here (see set_segfault()).

Will