Hi Henry,
On 08/12/2022 03:06, Henry Wang wrote:
I am trying to work on the follow-up improvements about the Arm P2M code,
and while trying to address the comment below, I noticed there was an unfinished
discussion between me and Julien which I would like to continue and here
opinions from all of you (if possible).
-----Original Message-----
From: Julien Grall <jul...@xen.org>
Subject: Re: [PATCH v2] xen/arm: p2m: Populate pages for GICv2 mapping in
arch_domain_create()
I also noticed that relinquish_p2m_mapping() is not called. This should
be fine for us because arch_domain_create() should never create a
mapping that requires p2m_put_l3_page() to be called.
For the background of the discussion, this was about the failure path of
arch_domain_create(), where we only call p2m_final_teardown() which does
not call relinquish_p2m_mapping()...
So all this mess with the P2M is necessary because we are mapping the
GICv2 CPU interface in arch_domain_create(). I think we should consider
to defer the mapping to later.
Other than it makes the code simpler, it also means we could also the
P2M root on the same numa node the domain is going to run (those
information are passed later on).
There is a couple of options:
1. Introduce a new hypercall to finish the initialization of a domain
(e.g. allocating the P2M and map the GICv2 CPU interface). This option
was briefly discussed with Jan (see [2])./
2. Allocate the P2M when populate the P2M pool and defer the GICv2 CPU
interface mapping until the first access (similar to how with deal with
MMIO access for ACPI).
I find the second option is neater but it has the drawback that it
requires on more trap to the hypervisor and we can't report any mapping
failure (which should not happen if the P2M was correctly sized). So I
am leaning towards option 2.
Any opinions?
Cheers,
[1]
https://lore.kernel.org/xen-devel/6c07cdfc-888a-45bb-2077-528a809a6...@suse.com/
--
Julien Grall
