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

Alex Williamson
2023-06-13T20:10:58Z

On Tue, 13 Jun 2023 14:35:09 -0300
Jason Gunthorpe <jgg@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,

Alex