Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU drivers

[Jason Gunthorpe]

On Mon, Oct 07, 2024 at 09:36:18AM -0700, Nicolin Chen wrote:
> On Mon, Oct 07, 2024 at 12:38:37PM -0300, Jason Gunthorpe wrote:
> > On Fri, Oct 04, 2024 at 10:19:43PM -0700, Nicolin Chen wrote:
> > > I tried exposing the struct iommufd_viommu to drivers, and was
> > > able to drop a couple of helpers, except these two:
> > > 
> > > struct device *vdev_to_dev(struct iommufd_vdevice *vdev)
> > > {
> > > 	return vdev ? vdev->idev->dev : NULL;
> > > } // Without it, we need to expose struct iommufd_device.
> > > 
> > > struct iommu_domain *
> > > iommufd_viommu_to_parent_domain(struct iommufd_viommu *viommu)
> > > {
> > > 	if (!viommu || !viommu->hwpt)
> > > 		return NULL;
> > > 	return viommu->hwpt->common.domain;
> > > } // Without it, we need to expose struct iommufd_hwpt_page.
> > 
> > It seems OK, there isn't really locking entanglements or performance
> > path on this stuff?
> 
> -----
> The typical use case of the first one is like:
> 	dev = vdev_to_dev(xa_load(&viommu->vdevs, (unsigned long)vdev_id));
> so I am asking for:
> /* Caller should lock via viommu->vdevs_rwsem with proper permission */

Why would vdev_to_dev need that locking? The viommu cannot change hwpt
during its lifecycle?

Jason