Re: [XEN v9 4/4] xen/arm64: io: Handle data abort due to cache maintenance instructions

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 01/03/2022 12:40, Ayan Kumar Halder wrote:
> When the data abort is caused due to cache maintenance for an address,
> there are two scenarios:-
>
> 1. Address belonging to a non emulated region - For this, Xen should
> set the corresponding bit in the translation table entry to valid and
> return to the guest to retry the instruction. This can happen sometimes
> as Xen need to set the translation table entry to invalid. (for eg
> 'Break-Before-Make' sequence).
>
> 2. Address belongs to an emulated region - Xen should ignore the
> instruction (ie increment the PC) and return to the guest.
I would be explicit and say something along the lines:

"Xen doesn't cache data for emulated regions. So we can safely ignore them".

There is a third scenarios:

The address belongs to neither an emulated region nor has a valid 
mapping in the P2M.
> We try to deal with scenario#1, by invoking check_p2m(). If this is
> unsuccessful, then we assume scenario#2.
This means that you will ignore cache maintenance on invalid region. I 
think we should send an abort to the guest rather than let them believe 
it worked.
Cheers,

--
Julien Grall