intel_iommu: Simplify caching mode check with VFIO device

In early days, we had different tricks to ensure caching-mode=on with VFIO
device:

28cf553afe ("intel_iommu: Sanity check vfio-pci config on machine init done")
c6cbc29d36 ("pc/q35: Disallow vfio-pci hotplug without VT-d caching mode")

There is also a patch with the same purpose but for VDPA device:

b8d78277c0 ("intel-iommu: fail MAP notifier without caching mode")

Because without caching mode, MAP notifier won't work correctly since guest
won't send IOTLB update event when it establishes new mappings in the I/O page
tables.

Now with host IOMMU device interface between VFIO and vIOMMU, we can simplify
first two commits above with a small check in set_iommu_device(). This also
works for future IOMMUFD backed VDPA implementation which may also need caching
mode on. But for legacy VDPA we still need commit b8d78277c0 as it doesn't
use the host IOMMU device interface.

For coldplug VFIO device:

  qemu-system-x86_64: -device vfio-pci,host=0000:3b:00.0,id=hostdev3,bus=root0,iommufd=iommufd0: vfio 0000:3b:00.0: Failed to set vIOMMU: Device assignment is not allowed without enabling caching-mode=on for Intel IOMMU.

For hotplug VFIO device:

  if "iommu=off" is configured in guest,
    Error: vfio 0000:3b:00.0: Failed to set vIOMMU: Device assignment is not allowed without enabling caching-mode=on for Intel IOMMU.
  else
    Error: vfio 0000:3b:00.0: memory listener initialization failed: Region vtd-00.0-dmar: device 01.00.0 requires caching mode: Operation not supported

The specialty for hotplug is due to the check in commit b8d78277c0 happen before
the check in set_iommu_device.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250929034206.439266-3-zhenzhong.duan@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

0 files changed, 0 insertions, 0 deletions