By default, NVMe data transfer operations use a scatter-gather list in
which all entries point to a fixed-size memory region. For example, if
the memory page size is 4KB, a 2MB IO requires 512 entries. Lists
themselves are also fixed in size (default is 512 entries).
Because the list size is fixed, the last entry is special. If the IO
requires more than 512 entries, the last entry in the list contains the
address of the next list of entries. But if the IO requires exactly 512
entries, the last entry points to data.
The NVMe emulation missed this logic and unconditionally treated the
last entry as a pointer to the next list.
