Re: [PATCH 6/7] xen/guest_access: Consolidate guest access helpers in xen/guest_access.h

[Jan Beulich <jbeulich@suse.com>]

On 04.04.2020 15:10, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> Most of the helpers to access guest memory are implemented the same way
> on Arm and x86. The only differences are:
>     - guest_handle_{from, to}_param(): while on x86 XEN_GUEST_HANDLE()
>       and XEN_GUEST_HANDLE_PARAM() are the same, they are not on Arm. It
>       is still fine to use the Arm implementation on x86.
>     - __clear_guest_offset(): Interestingly the prototype does not match
>       between the x86 and Arm. However, the Arm one is bogus. So the x86
>       implementation can be used.
>     - guest_handle{,_subrange}_okay(): They are validly differing
>       because Arm is only supporting auto-translated guest and therefore
>       handles are always valid.

While I'm fine in principle with such consolidation, I'm afraid I
really need to ask for some historical background to be added
here. It may very well be that there's a reason for the separation
(likely to be found in the removed ia64 or ppc ports), which may
then provide a hint at why future ports may want to have these
separated. If such reasons exist, I'd prefer to avoid the back and
forth between headers. What we could do in such a case is borrow
Linux'es asm-generic/ concept, and move the "typical"
implementation there. (And of course if there were no noticable
reasons for the split, the change as it is would be fine in
general; saying so without having looked at the details of it,
yet).

Jan