Re: [PATCH 5/8] x86/entry: Adjust restore_all_xen to hold stack_end in %r14

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/09/2023 9:51 am, Jan Beulich wrote:
> On 13.09.2023 22:27, Andrew Cooper wrote:
>> All other SPEC_CTRL_{ENTRY,EXIT}_* helpers hold stack_end in %r14.  Adjust it
>> for consistency, freeing up %rbx to be used differently.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> The choice of %rbx was, iirc, for avoiding unnecessary code size increase
> (due to extra REX prefixes needed in some of the affected insns). I
> understand you view this as not a real concern, but I think saying so
> explicitly in the description would be at least desirable. After all there
> would also be the alternative of further parametrizing the involved macros.

Yeah I'm seriously not concerned about a REX prefix or two.

This is about making all the helpers more consistent, to cut down on the
number of errors involved in modifying this mess.

~Andrew