Re: [PATCH] xen/arm: p2m: Populate pages for GICv2 mapping in arch_domain_create()

[Julien Grall <julien@xxxxxxx>]

Hi Xenia,

On 14/10/2022 10:46, Xenia Ragiadakou wrote:
> On 10/13/22 15:39, Julien Grall wrote:
> > Hi,
> >
> > On 13/10/2022 13:29, Henry Wang wrote:
> > > > -----Original Message-----
> > > > From: Jan Beulich <jbeulich@xxxxxxxx>
> > > > > > Assuming you have 4 (N) page table levels, isn't it 7 (1 + 2 * (N 
> > > > > > - 1))?
> > > > > > Or is the root table not taken from the p2m pool?
> > > > > Correct, on arm the root is not taken from the pool.
> > > > Isn't that a (perhaps just minor) mistake?
> > > Not really, in the code review phase, the question of whether we include
> > > the root in the p2m pool was discussed and the conclusion at that time
> > > was not including this page for now, as this is supposed to require a 
> > > lot
> > > of extra work/refactor. Probably there will be a series from my side to
> > > add the root to the pool, but at least not now.
> > The root page tables can be one of multiple concatenated pages (up to 
> > 8 pages). The P2M pool is allocating page by page and therefore 
> > wouldn't allow us to allocate contiguous pages.
> Sorry that I 'm asking this so late (I was just going through the 
> thread) but why 8?
Rather than providing an extra level of page-tables, the architecture 
allows you to provide multiple pages at the root level.
The number of concatenated pages depend on the maximum physical address 
and the start level. You can look at the table in setup_virt_paging() 
for more details.
Cheers,

--
Julien Grall