Re: [PATCH v2 2/2] xen/arm: gnttab: modify macros to evaluate all arguments and only once

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 17/05/2022 08:14, Michal Orzel wrote:
> On 16.05.2022 12:19, Julien Grall wrote:
> > Hi Michal,
> >
> > On 06/05/2022 10:42, Michal Orzel wrote:
> > > Modify macros to evaluate all the arguments and make sure the arguments
> > > are evaluated only once. Introduce following intermediate macros:
> > > gnttab_status_gfn_, gnttab_shared_gfn_ that do not take domain as a
> > > parameter. These are to be used locally and allow us to avoid passing
> > > NULL from gnttab_get_frame_gfn to the respective macros (without _ suffix).
> > > Make use of a domain parameter from gnttab_shared_gfn and gnttab_status_gfn
> > > by adding an ASSERT.
> > >
> > > Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> > Most of the helpers below are going to disappear with Oleksandr latest work 
> > (see [1]).
> >
> > Looking at Oleksandr's patch, I think only gnttab_set_frame_gfn() would end up 
> > to use one of the macro parameters twice. So I would like to suggest to chat 
> > with Oleksandr if we can tweak his patch (can be done on commit) or we rebase 
> > this patch on top of his work.
> >
> > Cheers,
> >
> > [1] 
> > https://lore.kernel.org/xen-devel/1652294845-13980-1-git-send-email-olekstysh@xxxxxxxxx/
> By looking at Oleksandr patch:
> 1. there are 2 macros: gnttab_set_frame_gfn, gnttab_need_iommu_mapping that use 
> one of the macro parameters twice.
> 2. gnttab_get_frame_gfn still passes NULL as a domain parameter to 
> gnttab_shared_gfn/gnttab_status_gfn that do not evaluate domain parameter
>
> I agree that point 1 could be fixed on commit but point 2 requires in my 
> opinion adding intermediate macros to avoid passing NULL (just like I did).
Ok. I think we could avoid the intermediate macros by implementing the 
helpers the other way around. I.e gnttab_{status}_gfn() call 
gnttab_get_frame_gfn().
> As this would require more work from Oleksandr, I'm ok to rebase my patch on 
> top of his work once merged.
Thanks!

Cheers,

--
Julien Grall