Hi Stefano,
On 12/05/2021 23:44, Stefano Stabellini wrote:
On Sun, 25 Apr 2021, Julien Grall wrote:
From: Julien Grall <jgr...@amazon.com>
xen_{un,}map_table() already uses the helper to map/unmap pages
on-demand (note this is currently a NOP on arm64). So switching to
domheap don't have any disavantage.
But this as the benefit:
- to keep the page tables unmapped if an arch decided to do so
- reduce xenheap use on arm32 which can be pretty small
Signed-off-by: Julien Grall <jgr...@amazon.com>
Thanks for the patch. It looks OK but let me ask a couple of questions
to clarify my doubts.
This change should have no impact to arm64, right?
For arm32, I wonder why we were using map_domain_page before in
xen_map_table: it wasn't necessary, was it? In fact, one could even say
that it was wrong?
In xen_map_table() we need to be able to map pages from Xen binary,
xenheap... On arm64, we would be able to use mfn_to_virt() because
everything is mapped in Xen. But that's not the case on arm32. So we
need a way to map anything easily.
The only difference between xenheap and domheap are the former is always
mapped while the latter may not be. So one can also view a xenheap page
as a glorified domheap.
I also don't really want to create yet another interface to map pages
(we have vmap(), map_domain_page(), map_domain_global_page()...). So,
when I implemented xen_map_table() a couple of years ago, I came to the
conclusion that this is a convenient (ab)use of the interface.
Cheers,
--
Julien Grall
