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

[Liu, Yi L]

> 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.

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);
}
#else
blabla
#endif

Regards,
Yi Liu