scsi: vmw_pvscsi: Set residual data length conditionally

The PVSCSI implementation in the VMware hypervisor under specific
configuration ("SCSI Bus Sharing" set to "Physical") returns zero dataLen
in the completion descriptor for READ CAPACITY(16). As a result, the kernel
can not detect proper disk geometry. This can be recognized by the kernel
message:

  [ 0.776588] sd 1:0:0:0: [sdb] Sector size 0 reported, assuming 512.

The PVSCSI implementation in QEMU does not set dataLen at all, keeping it
zeroed. This leads to a boot hang as was reported by Shmulik Ladkani.

It is likely that the controller returns the garbage at the end of the
buffer. Residual length should be set by the driver in that case. The SCSI
layer will erase corresponding data. See commit bdb2b8c ("[SCSI] erase
invalid data returned by device") for details.

Commit e662502 ("scsi: vmw_pvscsi: Set correct residual data length")
introduced the issue by setting residual length unconditionally, causing
the SCSI layer to erase the useful payload beyond dataLen when this value
is returned as 0.

As a result, considering existing issues in implementations of PVSCSI
controllers, we do not want to call scsi_set_resid() when dataLen ==
0. Calling scsi_set_resid() has no effect if dataLen equals buffer length.

Link: https://lore.kernel.org/lkml/20210824120028.30d9c071@blondie/
Link: https://lore.kernel.org/r/[email protected]
Fixes: e662502 ("scsi: vmw_pvscsi: Set correct residual data length")
Cc: Matt Wang <[email protected]>
Cc: Martin K. Petersen <[email protected]>
Cc: Vishal Bhakta <[email protected]>
Cc: VMware PV-Drivers <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reported-and-suggested-by: Shmulik Ladkani <[email protected]>
Signed-off-by: Alexey Makhalov <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Alexey Makhalov

drivers/scsi/vmw_pvscsi.c

@@ -586,9 +586,12 @@ static void pvscsi_complete_request(struct pvscsi_adapter *adapter,
 			 * Commands like INQUIRY may transfer less data than
 			 * requested by the initiator via bufflen. Set residual
 			 * count to make upper layer aware of the actual amount
-			 * of data returned.
+			 * of data returned. There are cases when controller
+			 * returns zero dataLen with non zero data - do not set
+			 * residual count in that case.
 			 */
-			scsi_set_resid(cmd, scsi_bufflen(cmd) - e->dataLen);
+			if (e->dataLen && (e->dataLen < scsi_bufflen(cmd)))
+				scsi_set_resid(cmd, scsi_bufflen(cmd) - e->dataLen);
 			cmd->result = (DID_OK << 16);
 			break;