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

[Tian, Kevin]

> 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.

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);

	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