block: fix max segment size handling in blk_queue_virt_boundary

We should only set the max segment size to unlimited if we actually
have a virt boundary.  Otherwise we accidentally clear that limit
when called from the SCSI midlayer, which always calls
blk_queue_virt_boundary, even if that mask is 0.

Fixes: 7ad388d8 ("scsi: core: add a host / host template field for the virt boundary")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-settings.c

@@ -752,6 +752,7 @@ void blk_queue_virt_boundary(struct request_queue *q, unsigned long mask)
 	 * page (which might not be idential to the Linux PAGE_SIZE).  Because
 	 * of that they are not limited by our notion of "segment size".
 	 */
+	if (mask)
 		q->limits.max_segment_size = UINT_MAX;
 }
 EXPORT_SYMBOL(blk_queue_virt_boundary);