Re: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround

[Arnd Bergmann]

On Tue, May 10, 2022 at 1:53 PM Verdun, Jean-Marie <verdun@xxxxxxx> wrote:
>
> Hi Arnd,
>
> >    Hi Nick,
>
> >    This seems a bit more complex than necessary. Can't you just use a custom
> >    inline asm with an ex_table entry to catch the fault? Have a look at
> >    __get_user_asm() for an example.
> >
> >           Arnd
>
> We got inspired from debug_reg_hook within the same source file
>( ./arch/arm/kernel/hw_breakpoint.c ). We chose that path to keep coherency
> within the source code. We can implement the same fix by using an ex_table
> entry, but this will create two different ways at catching unknown instruction
> within the same source file. Will that be ok ?

I got a little lost trying to find where the breakpoint instruction comes
from that gets trapped here, but I would guess that they had to do this
using an undef_hook because the ex_table approach does not work
there for some reason.

I would still pick the ex_table method here if that works.

       Arnd