On Wed, Jan 15, 2020 at 09:53:27AM -0700, Jens Axboe wrote: > We'd need it in a union for this to work. Note that union usage may be a bit problematic, as it may lead to difference in behaviour (and possible subtle bugs, as a result) between native 32-bit kernel and 64-bit one in compat mode due to the fact that u64_to_user_ptr doesn't check higher 32 bits on 32 bit kernels; it is mostly ignored in the case of plain __u64 usage, as it is less likely to pass garbage in the higher 32 bits in that case, but the issue, nevertheless, stands, so I'd propose to check these bits in case the union approach is implemented.
