iommufd/viommu: Publish a vDEVICE only after vdevice_init() succeeds

iommufd_vdevice_alloc_ioctl() adds the vDEVICE to the viommu->vdevs xarray
with xa_cmpxchg() before the driver's vdevice_init() op runs. That op is
where a driver validates the device and may reject it, but the xarray entry
is already live by then: a concurrent IOMMU_HWPT_INVALIDATE can look it up
with iommufd_viommu_find_dev() and run the driver invalidation path against
a device that vdevice_init() would have refused.

Reserve the index with xa_insert(): it stores a zero entry that reads back
as NULL, and returns -EBUSY on a duplicate virt_id. Run vdevice_init() and
store the vDEVICE pointer only once it succeeds. A failed vdevice_init()
releases the reservation, so lookups observe the vDEVICE only after it is
fully initialized and accepted.

Fixes: ed42eee797ff3 ("iommufd/viommu: Add driver-defined vDEVICE support")
Link: https://patch.msgid.link/r/1e05999347f4bf583edbc6a1312c857d5548708c.1783311134.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

0 files changed, 0 insertions, 0 deletions