On Tue, Feb 18, 2025 at 11:29:59AM -0400, Jason Gunthorpe wrote:
> On Fri, Jan 24, 2025 at 04:30:34PM -0800, Nicolin Chen wrote:
> > + list_add_tail(&vevent->node, &eventq->deliver);
> > + vevent->on_list = true;
> > + vevent->header.sequence = atomic_read(&veventq->sequence);
> > + if (atomic_read(&veventq->sequence) == INT_MAX)
> > + atomic_set(&veventq->sequence, 0);
> > + else
> > + atomic_inc(&veventq->sequence);
> > + spin_unlock(&eventq->lock);
>
> This is all locked, we don't need veventq->sequence to be an atomic?
>
> The bounding can be done with some simple math:
>
> veventq->sequence = (veventq->sequence + 1) & INT_MAX;
Ack. Perhaps we can reuse eventq->lock to fence @num_events too.
> > +static struct iommufd_vevent *
> > +iommufd_veventq_deliver_fetch(struct iommufd_veventq *veventq)
> > +{
> > + struct iommufd_eventq *eventq = &veventq->common;
> > + struct list_head *list = &eventq->deliver;
> > + struct iommufd_vevent *vevent = NULL;
> > +
> > + spin_lock(&eventq->lock);
> > + if (!list_empty(list)) {
> > + vevent = list_first_entry(list, struct iommufd_vevent, node);
> > + list_del(&vevent->node);
> > + vevent->on_list = false;
> > + }
> > + /* Make a copy of the overflow node for copy_to_user */
> > + if (vevent == &veventq->overflow) {
> > + vevent = kzalloc(sizeof(*vevent), GFP_ATOMIC);
> > + if (vevent)
> > + memcpy(vevent, &veventq->overflow, sizeof(*vevent));
> > + }
>
> This error handling is wonky, if we can't allocate then we shouldn't
> have done the list_del. Just return NULL which will cause
> iommufd_veventq_fops_read() to exist and userspace will try again.
OK.
We have two cases to support here:
1) Normal vevent node -- list_del and return the node.
2) Overflow node -- list_del and return a copy.
I think we can do:
if (!list_empty(list)) {
struct iommufd_vevent *next;
next = list_first_entry(list, struct iommufd_vevent, node);
if (next == &veventq->overflow) {
/* Make a copy of the overflow node for copy_to_user */
vevent = kzalloc(sizeof(*vevent), GFP_ATOMIC);
if (!vevent)
goto out_unlock;
}
list_del(&next->node);
if (vevent)
memcpy(vevent, next, sizeof(*vevent));
else
vevent = next;
}
> > @@ -403,6 +531,10 @@ static int iommufd_eventq_fops_release(struct inode
> > *inode, struct file *filep)
> > {
> > struct iommufd_eventq *eventq = filep->private_data;
> >
> > + if (eventq->obj.type == IOMMUFD_OBJ_VEVENTQ) {
> > + atomic_set(&eventq_to_veventq(eventq)->sequence, 0);
> > + atomic_set(&eventq_to_veventq(eventq)->num_events, 0);
> > + }
>
> Why? We are about to free the memory?
Ack. I thought about a re-entry of an open(). But release() does
lose the event_fd completely, and user space wouldn't be able to
open the same fd again.
> > +int iommufd_veventq_alloc(struct iommufd_ucmd *ucmd)
> > +{
> > + struct iommu_veventq_alloc *cmd = ucmd->cmd;
> > + struct iommufd_veventq *veventq;
> > + struct iommufd_viommu *viommu;
> > + int fdno;
> > + int rc;
> > +
> > + if (cmd->flags || cmd->type == IOMMU_VEVENTQ_TYPE_DEFAULT)
> > + return -EOPNOTSUPP;
> > + if (!cmd->veventq_depth)
> > + return -EINVAL;
>
> Check __reserved for 0 too
Kevin is suggesting a 32-bit flag field, so I think we can drop
the __reserved in that case.
Thanks
Nicolin
