[Intel-gfx] [PATCH v12 21/24] vfio: Determine noiommu device in __vfio_register_dev()

[Liu, Yi L]

> From: Tian, Kevin <kevin.tian at intel.com>
> Sent: Wednesday, June 14, 2023 1:42 PM
> 
> > From: Liu, Yi L <yi.l.liu at intel.com>
> > Sent: Wednesday, June 14, 2023 11:24 AM
> >
> > > From: Alex Williamson <alex.williamson at redhat.com>
> > > Sent: Wednesday, June 14, 2023 4:11 AM
> > >
> > > On Tue, 13 Jun 2023 14:35:09 -0300
> > > Jason Gunthorpe <jgg at nvidia.com> wrote:
> > >
> > > > On Tue, Jun 13, 2023 at 11:15:11AM -0600, Alex Williamson wrote:
> > > > > [Sorry for breaking threading, replying to my own message id with reply
> > > > >  content from Yi since the Cc list got broken]
> > > >
> > > > Yikes it is really busted, I think I fixed it?
> > > >
> > > > > If we renamed your function above to vfio_device_has_iommu_group(),
> > > > > couldn't we just wrap device_add like below instead to not have cdev
> > > > > setup for a noiommu device, generate an error for a physical device
> > w/o
> > > > > IOMMU backing, and otherwise setup the cdev device?
> > > > >
> > > > > static inline int vfio_device_add(struct vfio_device *device, enum
> > vfio_group_type
> > > type)
> > > > > {
> > > > > #if IS_ENABLED(CONFIG_VFIO_GROUP)
> > > > > 	if (device->group->type == VFIO_NO_IOMMU)
> > > > > 		return device_add(&device->device);
> > > >
> > > > vfio_device_is_noiommu() embeds the IS_ENABLED
> > >
> > > But patch 23/ makes the definition of struct vfio_group conditional on
> > > CONFIG_VFIO_GROUP, so while CONFIG_VFIO_NOIOMMU depends on
> > > CONFIG_VFIO_GROUP and the result could be determined, I think the
> > > compiler is still unhappy about the undefined reference.  We'd need a
> > > !CONFIG_VFIO_GROUP stub for the function.
> > >
> > > > > #else
> > > > > 	if (type == VFIO_IOMMU && !vfio_device_has_iommu_group(device))
> > > > > 		return -EINVAL;
> > > > > #endif
> > > >
> > > > The require test is this from the group code:
> > > >
> > > >  	if (!device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY))
> > {
> > > >
> > > > We could lift it out of the group code and call it from vfio_main.c like:
> > > >
> > > > if (type == VFIO_IOMMU && !vfio_device_is_noiommu(vdev)
> > > && !device_iommu_capable(dev,
> > > >      IOMMU_CAP_CACHE_COHERENCY))
> > > >    FAIL
> > >
> > > Ack.  Thanks,
> >
> > So, what I got is:
> >
> > 1) Add bellow check in __vfio_register_dev() to fail the physical devices that
> >     don't have IOMMU protection.
> >
> > 	/*
> > 	  * noiommu device is a special type supported by the group interface.
> > 	  * Such type represents the physical devices  that are not iommu
> > backed.
> > 	  */
> > 	if (type == VFIO_IOMMU && !vfio_device_is_noiommu(device)) &&
> > 	    !vfio_device_has_iommu_group(device))
> > 		return -EINVAL; //or maybe -EOPNOTSUPP?
> >
> > Nit: require a vfio_device_is_noiommu() stub which returns false for
> > the VFIO_GROUP unset case.
> 
> device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY) is valid
> only for cases with iommu groups. So that check already  covers the
> group verification indirectly.

Okay. This IOMMU_CAP_CACHE_COHERENCY check is missed in the cdev
path.

> With that I think Jason's suggestion is to lift that test into main.c:
> 
> int vfio_register_group_dev(struct vfio_device *device)
> {
> 	/*
> 	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
> 	 * restore cache coherency. It has to be checked here because it is only
> 	 * valid for cases where we are using iommu groups.
> 	 */
> 	if (type == VFIO_IOMMU && !vfio_device_is_noiommu(device) &&
> 	    !device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY))
> 		return ERR_PTR(-EINVAL);

vfio_device_is_noiommu() needs to be called after vfio_device_set_group().
Otherwise, it's always false. So still needs to call it in the __vfio_register_dev().

> 	return __vfio_register_dev(device, VFIO_IOMMU);
> }
> 
> >
> > 2) Have below functions to add device
> >
> > #if IS_ENABLED(CONFIG_VFIO_DEVICE_CDEV)
> > static inline int vfio_device_add(struct vfio_device *device)
> > {
> > 	if (vfio_device_is_noiommu(device))
> > 		return device_add(&device->device);
> > 	vfio_init_device_cdev(device);
> > 	return cdev_device_add(&device->cdev, &device->device);
> > }
> >
> > static inline void vfio_device_del(struct vfio_device *device)
> > {
> > 	if (vfio_device_is_noiommu(device))
> > 		return device_del(&device->device);
> > 	cdev_device_del(&device->cdev, &device->device);
> > }
> 
> Correct

Regards,
Yi Liu