iommu/sva: Fix crash in iommu_sva_unbind_device()

iommu/sva: Fix crash in iommu_sva_unbind_device()

[ Upstream commit 06e14c36e20b48171df13d51b89fe67c594ed07a ]

domain->mm->iommu_mm can be freed by iommu_domain_free():
  iommu_domain_free()
    mmdrop()
      __mmdrop()
        mm_pasid_drop()
After iommu_domain_free() returns, accessing domain->mm->iommu_mm may
dereference a freed mm structure, leading to a crash.

Fix this by moving the code that accesses domain->mm->iommu_mm to before
the call to iommu_domain_free().

Fixes: e37d5a2d60a3 ("iommu/sva: invalidate stale IOTLB entries for kernel address space")
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>