On Sat, Mar 28, 2020 at 11:13 AM Keith Busch [off-list ref] wrote:

On Sat, Mar 28, 2020 at 10:11:57AM +0800, Ming Lei wrote:

quoted

On Sat, Mar 28, 2020 at 2:18 AM Keith Busch [off-list ref] wrote:

quoted

This is actually even more confusing. We do not support 256MB transfers
within a single command in the pci nvme driver anymore. The max is 4MB,
so I don't see how increasing the max segments will help: you should be
hitting the 'max_sectors' limit if you don't hit the segment limit first.

That looks a bug for passthrough req, because 'max_sectors' limit is only
checked in bio_add_pc_page(), not done in blk_rq_append_bio(), something
like the following seems required:

Shouldn't bio_map_user_iov() or bio_copy_user_iov() have caught the
length limit before proceeding to blk_rq_append_bio()?

Actually the limit should be caught earlier in bio_add_pc_page(), that requires
to pass 'rq' in, then one perfect passthrough bio can be made before
appending to rq.

Not only max sector limit, max segments & virt_boundary should be checked
in request wide too.

So far, only lightnvm calls bio_add_pc_page() before allocating
request, and that is
the 1st bio, so NULL rq can be passed.

thanks,
Ming Lei