iommufd: Remove IOMMUFD_PAGE_RESP_FAILURE

The response code of IOMMUFD_PAGE_RESP_FAILURE was defined to be
equivalent to the "Response Failure" in PCI spec, section 10.4.2.1.
This response code indicates that one or more pages within the
associated request group have encountered or caused an unrecoverable
error. Therefore, this response disables the PRI at the function.

Modern I/O virtualization technologies, like SR-IOV, share PRI among
the assignable device units. Therefore, a response failure on one unit
might cause I/O failure on other units.

Remove this response code so that user space can only respond with
SUCCESS or INVALID. The VMM is recommended to emulate a failure response
as a PRI reset, or PRI disable and changing to a non-PRI domain.

Fixes: c714f15 ("iommufd: Add fault and response message definitions")
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Lu Baolu <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: LuBaolu

include/uapi/linux/iommufd.h

@@ -765,14 +765,10 @@ struct iommu_hwpt_pgfault {
  * @IOMMUFD_PAGE_RESP_INVALID: Could not handle this fault, don't retry the
  *                             access. This is the "Invalid Request" in PCI
  *                             10.4.2.1.
- * @IOMMUFD_PAGE_RESP_FAILURE: General error. Drop all subsequent faults from
- *                             this device if possible. This is the "Response
- *                             Failure" in PCI 10.4.2.1.
  */
 enum iommufd_page_response_code {
 	IOMMUFD_PAGE_RESP_SUCCESS = 0,
 	IOMMUFD_PAGE_RESP_INVALID,
-	IOMMUFD_PAGE_RESP_FAILURE,
 };
 
 /**