Re: [PATCH v4 2/3] xen/mm: allow deferred scrub of physmap populate allocated pages

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jan 28, 2026 at 03:34:11PM +0100, Jan Beulich wrote:
> On 28.01.2026 14:33, Roger Pau Monné wrote:
> > On Wed, Jan 28, 2026 at 12:44:26PM +0000, Andrew Cooper wrote:
> >> In principle we could assert that it's already NULL in _domain_destroy()
> >> which might help catch an error if it gets set early but the domain
> >> destroyed before getting into the domlist, but that seems like a rather
> >> slim case.
> > 
> > Given my understanding of the logic in the XENMEM_ hypercalls, I think
> > toolstack can still target domains in the process of being destroyed,
> > at which point we need to keep a final cleanup instance
> > _domain_destroy(), or otherwise adjust XENMEM_populate_physmap
> > hypercall (and others?) so they can't target dying domains.
> 
> Considering that these requests will fail for dying domains because of the
> check in assign_pages(), it may indeed make sense to have another earlier
> check for the purposes here. Otoh doing this early may not buy us very
> much, as the domain may become "dying" immediately after the check. Whereas
> switching stash_allocation()'s if() to
> 
>     if ( d->pending_scrub || d->is_dying )
> 
> looks like it might do.

Oh, I didn't notice the check in assign_pages().

I think a check in stash_allocation() together with a call to
domain_pending_scrub_free() in domain_teardown() (which is after
setting d->is_dying) should be enough to ensure the field is clear
when reaching _domain_destroy().  The call to
domain_pending_scrub_free() in _domain_destroy() can be replaced with
an ASSERT(!d->pending_scrub) then.

Thanks, Roger.