Referencing domain struct from interrupt handler

[Jens Wiklander <jens.wiklander@xxxxxxxxxx>]

Hi Xen maintainers,

In my patch series [XEN PATCH v4 0/5] FF-A notifications [1] I need to
get a reference to a domain struct from a domain ID and keep it from
being destroyed while using it in the interrupt handler
notif_irq_handler() (introduced in the last patch "[XEN PATCH v4 5/5]
xen/arm: ffa: support notification"). In my previous patch set [2] I
used get_domain_by_id(), but from the following discussion
rcu_lock_live_remote_domain_by_id() seems to be a better choice so
that's what I'm using now in the v4 patch set. The domain lock is held
during a call to vgic_inject_irq() and unlocked right after.

While we're reviewing the patch set in [1] I'd like to check the
approach with rcu_lock_live_remote_domain_by_id() here.

What do you think? Is using rcu_lock_live_remote_domain_by_id() the
best approach?

[1] https://patchew.org/Xen/20240502145645.1201613-1-jens.wiklander@xxxxxxxxxx/
[2] https://patchew.org/Xen/20240426084723.4149648-1-jens.wiklander@xxxxxxxxxx/

Thanks,
Jens