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

[Baolu Lu]

On 12/11/23 11:24 PM, Jason Gunthorpe wrote:
> On Thu, Dec 07, 2023 at 02:43:08PM +0800, Lu Baolu wrote:
> > @@ -217,12 +250,9 @@ int iommu_page_response(struct device *dev,
> >   	if (!ops->page_response)
> >   		return -ENODEV;
> >   
> > -	mutex_lock(&param->lock);
> > -	fault_param = param->fault_param;
> > -	if (!fault_param) {
> > -		mutex_unlock(&param->lock);
> > +	fault_param = iopf_get_dev_fault_param(dev);
> > +	if (!fault_param)
> >   		return -EINVAL;
> > -	}
> The refcounting should work by passing around the fault_param object,
> not re-obtaining it from the dev from a work.
>
> The work should be locked to the iommu_fault_param that was active
> when the work was launched.
>
> When we get to iommu_page_response it does this:
>
> 	/* 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;
> 	}
>
> Which determines that the iommu_fault_param is stale and pending
> free..

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;

	/* 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);

	return ret;
}

...

void iopf_free_group(struct iopf_group *group)
{
	struct iopf_fault *iopf, *next;

	list_for_each_entry_safe(iopf, next, &group->faults, list) {
		if (!(iopf->fault.prm.flags & IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
			kfree(iopf);
	}

	/* Pair with iommu_report_device_fault(). */
	iopf_put_dev_fault_param(group->fault_param);
	kfree(group);
}

Best regards,
baolu