iommu/amd: Clear DMA ops when switching domain

Since commit 08a27c1c ("iommu: Add support to change default domain
of an iommu group") a user can switch a device between IOMMU and direct
DMA through sysfs. This doesn't work for AMD IOMMU at the moment because
dev->dma_ops is not cleared when switching from a DMA to an identity
IOMMU domain. The DMA layer thus attempts to use the dma-iommu ops on an
identity domain, causing an oops:

  # echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/unbind
  # echo identity > /sys/bus/pci/devices/0000:00:05.0/iommu_group/type
  # echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/bind
   ...
  BUG: kernel NULL pointer dereference, address: 0000000000000028
   ...
   Call Trace:
    iommu_dma_alloc
    e1000e_setup_tx_resources
    e1000e_open

Since iommu_change_dev_def_domain() calls probe_finalize() again, clear
the dma_ops there like Vt-d does.

Fixes: 08a27c1c ("iommu: Add support to change default domain of an iommu group")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20210422094216.2282097-1-jean-philippe@linaro.orgSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd/iommu.c

@@ -1714,6 +1714,8 @@ static void amd_iommu_probe_finalize(struct device *dev)
 	domain = iommu_get_domain_for_dev(dev);
 	if (domain->type == IOMMU_DOMAIN_DMA)
 		iommu_setup_dma_ops(dev, IOVA_START_PFN << PAGE_SHIFT, 0);
+	else
+		set_dma_ops(dev, NULL);
 }
 
 static void amd_iommu_release_device(struct device *dev)