+	union {
+		struct {
+			void *meta; /* kernel-resident buffer */
+			void __user *meta_buffer;
+		};
+		struct {
+			u32 nvme_flags;
+			u32 nvme_status;
+			u64 result;
+		};
+	};

Without naming the arms of the union this is becoming a bit too much
of a mess..

+static void nvme_uring_task_cb(struct io_uring_cmd *ioucmd)
+{
+	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
+	int status;
+
+	if (pdu->nvme_flags & NVME_REQ_CANCELLED)
+		status = -EINTR;
+	else
+		status = pdu->nvme_status;

If you add a signed int field you only need one field instead of
two in the pdu for this (the nvme status is only 15 bits anyway).