Hi Penny,
On 27/06/2022 11:11, Penny Zheng wrote:
-----Original Message-----
From: Julien Grall <jul...@xen.org>
Sent: Saturday, June 25, 2022 3:51 AM
To: Penny Zheng <penny.zh...@arm.com>; xen-devel@lists.xenproject.org
Cc: Wei Chen <wei.c...@arm.com>; Andrew Cooper
<andrew.coop...@citrix.com>; George Dunlap <george.dun...@citrix.com>;
Jan Beulich <jbeul...@suse.com>; Stefano Stabellini <sstabell...@kernel.org>;
Wei Liu <w...@xen.org>
Subject: Re: [PATCH v7 9/9] xen: retrieve reserved pages on
populate_physmap
Hi Penny,
On 20/06/2022 03:44, Penny Zheng wrote:
When a static domain populates memory through populate_physmap at
runtime, it shall retrieve reserved pages from resv_page_list to make
sure that guest RAM is still restricted in statically configured memory
regions.
This commit also introduces a new helper acquire_reserved_page to make
it work.
Signed-off-by: Penny Zheng <penny.zh...@arm.com>
---
v7 changes:
- remove the lock, since we add the page to rsv_page_list after it has
been totally freed.
Hmmm... Adding the page after it has been totally freed doesn't mean you
can get away with the lock. AFAICT you can still have concurrent free/allocate
that could modify the list.
Therefore if you add/remove pages without the list, you would end up to
corrupt the list.
If you disagree, then please point out which lock (or mechanism) will prevent
concurrent access.
Ok. Combined with the last serie comments, actually, you suggest that we need
to add
two locks, right?
We at least need the second lock (i.e. d->page_alloc_lock). The first
lock (i.e.) may not be necessary if all the static memory are allocated
for a domain. So you can guarantee ordering by adding to the resv_page_list.
Unless there are an ordering issue between the locks, I would for now
suggest to keep both. We can refine this afterwards.
Cheers,
--
Julien Grall
