Re: [PATCH RFC v1 03/11] iommu/virtio: Handle incoming page faults

[Jean-Philippe Brucker]

Hi Vivek,

On Mon, Oct 11, 2021 at 01:41:15PM +0530, Vivek Gautam wrote:
> > > +     list_for_each_entry(ep, &viommu->endpoints, list) {
> > > +             if (ep->eid == endpoint) {
> > > +                     vdev = ep->vdev;
> 
> I have a question here though -
> Is endpoint-ID unique across all the endpoints available per 'viommu_dev' or
> per 'viommu_domain'?
> If it is per 'viommu_domain' then the above list is also incorrect.
> As you pointed to in the patch [1] -
> [PATCH RFC v1 02/11] iommu/virtio: Maintain a list of endpoints served
> by viommu_dev
> I am planning to add endpoint ID into a static global xarray in
> viommu_probe_device() as below:
> 
>         vdev_for_each_id(i, eid, vdev) {
>                 ret = xa_insert(&viommu_ep_ids, eid, vdev, GFP_KERNEL);
>                 if (ret)
>                         goto err_free_dev;
>         }
> 
> and replace the above list traversal as below:
> 
>                 xa_lock_irqsave(&viommu_ep_ids, flags);
>                 xa_for_each(&viommu_ep_ids, eid, vdev) {
>                         if (eid == endpoint) {
>                                 ret =
> iommu_report_device_fault(vdev->dev, &fault_evt);
>                                 if (ret)
>                                         dev_err(vdev->dev, "Couldn't
> handle page request\n");
>                         }
>                 }
>                 xa_unlock_irqrestore(&viommu_ep_ids, flags);
> 
> But using a global xarray would also be incorrect if the endpointsID are global
> across 'viommu_domain'.
> 
> I need to find the correct 'viommu_endpoint' to call iommu_report_device_fault()
> with the correct device.

The endpoint IDs are only unique across viommu_dev, so a global xarray
wouldn't work but one in viommu_dev would. In vdomain it doesn't work
either because we can't get to the domain from the fault handler without
first finding the endpoint

Thanks,
Jean