On Wed, May 18, 2022 at 08:27:31PM -0700, Eric Biggers wrote:

So the bio ends up with a total length that is a multiple of the logical block
size, but the lengths of the individual bvecs in the bio are *not* necessarily
multiples of the logical block size.  That's the problem.

I'm surely missing something here. I know the bvecs are not necessarily lbs
aligned, but why does that matter? Is there some driver that can only take
exactly 1 bvec, but allows it to be unaligned? If so, we could take the segment
queue limit into account, but I am not sure that we need to.
 

Note, there's also lots of code that assumes that bio_vec::bv_len is a multiple
of 512.  

Could you point me to some examples?

That was implied by it being a multiple of the logical block size.  But
the DMA alignment can be much lower, like 8 bytes (see nvme_set_queue_limits()).

That's the driver this was tested on, though I just changed it to 4 bytes for
5.19.