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

[Nicolin Chen]

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?

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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 */

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And for the second one:
/*
 * Convert a viommu to the encapsulated nesting parent domain. A caller must be
 * aware of the life cycle of the viommu pointer: only call this function in a
 * callback functions of viommu_alloc or a viommu op.
 */
-----

Thanks
Nicolin