On Wed, Jun 25, 2025 at 03:38:19AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Sent: Saturday, June 14, 2025 3:15 PM
> >
> > +int iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long
> > iova,
> > + unsigned long length)
> > {
> > struct iommufd_ioas *ioas =
> > container_of(iopt, struct iommufd_ioas, iopt);
> > struct iommufd_access *access;
> > unsigned long index;
> > + int ret = 0;
> >
> > xa_lock(&ioas->iopt.access_list);
> > xa_for_each(&ioas->iopt.access_list, index, access) {
> > + if (!access->ops || !access->ops->unmap) {
> > + ret = -EBUSY;
> > + goto unlock;
> > + }
>
> then accesses before this one have been notified to unpin the area
> while accesses afterwards are left unnotified.
>
> in the end the unmap fails but with some side-effect incurred.
>
> I'm not sure whether this intermediate state may lead to any undesired
> effect later. Just raise it in case you or Jason already thought about it.
That's a good point. When an access blocks the unmap, there is no
unmap happening so no point in notifying devices for ops->unmap.
And, when the function is re-entered, there could be a duplicated
ops->unmap call for those devices that are already notified once?
So, if we play safe, there can be a standalone xa_for_each to dig
for !access->ops->unmap. And it could be a bit cleaner to add an
iommufd_access_has_internal_use() to be called under those rwsems.
> > /* Something is not responding to unmap requests.
> > */
> > tries++;
> > - if (WARN_ON(tries > 100))
> > - return -EDEADLOCK;
> > + if (WARN_ON(tries > 100)) {
> > + rc = -EDEADLOCK;
> > + goto out_unmapped;
> > + }
>
> this looks an unrelated fix?
Yea.. let me separate it out.
Thanks
Nicolin
