nvme_disk: Add missing checks in the case where there is only one iovec.

May fix the remaining KDL in #16973.

src/add-ons/kernel/drivers/disk/nvme/nvme_disk.cpp

@@ -701,10 +701,11 @@ nvme_disk_io(void* cookie, io_request* request)
 			bounceAll = true;
 	}
 
-	// See if we need to bounce due to the first or last vec (which, unlike middle vecs,
+	// See if we need to bounce due to the first or last vecs.
-	// need only be a multiple of the block size, and must end and start on a page boundary,
-	// respectively, though the start address must always be 32-bit-aligned.)
 	if (nvme_request.iovec_count > 1) {
+		// There are middle vecs, so the first and last vecs have different restrictions: they
+		// need only be a multiple of the block size, and must end and start on a page boundary,
+		// respectively, though the start address must always be 32-bit-aligned.
 		physical_entry* entry = &nvme_request.iovecs[0];
 		if (!bounceAll && (((entry->address + entry->size) % B_PAGE_SIZE) != 0
 				|| (entry->address & 0x3) != 0 || (entry->size % block_size) != 0))
@@ -714,6 +715,12 @@ nvme_disk_io(void* cookie, io_request* request)
 		if (!bounceAll && ((entry->address % B_PAGE_SIZE) != 0
 				|| (entry->size % block_size) != 0))
 			bounceAll = true;
+	} else {
+		// There is only one vec. Check that it is a multiple of the block size,
+		// and that its address is 32-bit-aligned.
+		physical_entry* entry = &nvme_request.iovecs[0];
+		if (!bounceAll && ((entry->address & 0x3) != 0 || (entry->size % block_size) != 0))
+			bounceAll = true;
 	}
 
 	// See if we need to bounce due to rounding.