Re: [PATCH v8 12/12] iommu: Use refcount for fault data access

[Baolu Lu]

On 12/12/23 11:18 PM, Jason Gunthorpe wrote:
> On Tue, Dec 12, 2023 at 01:07:17PM +0800, Baolu Lu wrote:
>
> > Yes, agreed. The iopf_fault_param should be passed in together with the
> > iopf_group. The reference count should be released in the
> > iopf_free_group(). These two helps could look like below:
> >
> > int iommu_page_response(struct iopf_group *group,
> > 			struct iommu_page_response *msg)
> > {
> > 	bool needs_pasid;
> > 	int ret = -EINVAL;
> > 	struct iopf_fault *evt;
> > 	struct iommu_fault_page_request *prm;
> > 	struct device *dev = group->fault_param->dev;
> > 	const struct iommu_ops *ops = dev_iommu_ops(dev);
> > 	bool has_pasid = msg->flags & IOMMU_PAGE_RESP_PASID_VALID;
> > 	struct iommu_fault_param *fault_param = group->fault_param;
> >
> > 	if (!ops->page_response)
> > 		return -ENODEV;
>
> We should never get here if this is the case, prevent the device from
> being added in the first place

Yeah, could move it to iopf_queue_add_device(). WARN and return failure
there if the driver is not ready for page request handling.

> > 	/* Only send response if there is a fault report pending */
> > 	mutex_lock(&fault_param->lock);
> > 	if (list_empty(&fault_param->faults)) {
> > 		dev_warn_ratelimited(dev, "no pending PRQ, drop response\n");
> > 		goto done_unlock;
> > 	}
> > 	/*
> > 	 * Check if we have a matching page request pending to respond,
> > 	 * otherwise return -EINVAL
> > 	 */
> > 	list_for_each_entry(evt, &fault_param->faults, list) {
> > 		prm = &evt->fault.prm;
> > 		if (prm->grpid != msg->grpid)
> > 			continue;
> >
> > 		/*
> > 		 * If the PASID is required, the corresponding request is
> > 		 * matched using the group ID, the PASID valid bit and the PASID
> > 		 * value. Otherwise only the group ID matches request and
> > 		 * response.
> > 		 */
> > 		needs_pasid = prm->flags & IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID;
> > 		if (needs_pasid && (!has_pasid || msg->pasid != prm->pasid))
> > 			continue;
> >
> > 		if (!needs_pasid && has_pasid) {
> > 			/* No big deal, just clear it. */
> > 			msg->flags &= ~IOMMU_PAGE_RESP_PASID_VALID;
> > 			msg->pasid = 0;
> > 		}
> >
> > 		ret = ops->page_response(dev, evt, msg);
> > 		list_del(&evt->list);
> > 		kfree(evt);
> > 		break;
> > 	}
> >
> > done_unlock:
> > 	mutex_unlock(&fault_param->lock);
>
> I would have expected the group to free'd here? But regardless this
> looks like a good direction

Both work for me. We can decide it according to the needs of code later.

> Jason

Best regards,
baolu