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

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

On 10/14/22 13:04, Julien Grall wrote:
> 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.
I think you are referring to this:
[6] = { 52,      12/*12*/,  3,          3 },
Still I cannot understand why the maximum number of concatenated level 0 
translation tables for t0sz 12 and 4KB granule is 8 and not 16?
> Cheers,
--
Xenia