Re: [PATCH 2/2] xen/arm: Handle reserved heap pages in boot and heap allocator

[Julien Grall <julien@xxxxxxx>]

On 02/09/2022 04:30, Henry Wang wrote:
> Hi Julien,
Hi Henry,

> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > > > This code is now becoming quite confusing to understanding. This loop is
> > > > meant to map the xenheap. If I follow your documentation, it would
> > mean
> > > > that only the reserved region should be mapped.
> > > Yes I think this is the same question that I raised in the scissors line of the
> > > commit message of this patch.
> > Sorry I didn't notice the comment after the scissors line. This is the
> > same question :)
> >
> > > What I intend to do is still mapping the whole
> > > RAM because of the xenheap_* variables that you mentioned in...
> > >
> > > > More confusingly, xenheap_* variables will cover the full RAM.
> > > ...here. But only adding the reserved region to the boot allocator so the
> > > reserved region can become the heap later on. I am wondering if we
> > > have a more clear way to do that, any suggestions?
> > I think your code is correct. It only needs some renaming of the
> > existing variable (maybe to directmap_*?) to make clear the area is used
> > to access the RAM easily.
> Thanks for the clarification. I checked the code and found the xenheap_*
> variables are:
> xenheap_virt_start, xenheap_virt_end, xenheap_mfn_start,
> xenheap_mfn_end, xenheap_base_pdx.
>
> For clarification, do we need to change all of them to directmap_*?
Good question.

> A pure renaming should be easy (and I guess also safe), but maybe I am
> overthinking because arm32 also uses xenheap_virt_end, xenheap_mfn_start
> and xenheap_mfn_end. These variables refer to the real xenheap, I am not
> sure renaming these would reduce the readability for arm32.
So on arm32, only the xenheap is direct mapped today. So I think it 
would be fine to switch the name to "directmap_*". For extra clarify we 
could add an alias for arm32 between "xenheap_*" and "directmap_*".
Cheers,

--
Julien Grall