On Fri, Aug 03, 2018 at 01:58:46PM -0500, Benjamin Herrenschmidt wrote:

You are saying something along the lines of "I don't like an
instruction in your ISA, let's not support your entire CPU architecture
in Linux".

No.  I'm saying if you can't describe your architecture in the virtio
spec document it is bogus.

Our setup is not fucked. It makes a LOT of sense and it's a very
sensible design. It's hitting a problem due to a corner case oddity in
virtio bypassing the MMU, we've worked around such corner cases many
times in the past without any problem, I fail to see what the problem
is here.

No matter if you like it or not (I don't!) virtio is defined to bypass
dma translations, it is very clearly stated in the spec.  It has some
ill-defined bits to bypass it, so if you want the dma mapping API
to be used you'll have to set that bit (in its original form, a refined
form, or an entirely newly defined sane form) and make sure your
hypersivors always sets it.  It's not rocket science, just a little bit
for work to make sure your setup is actually going to work reliably
and portably.

We aren't going to cancel years of HW and SW development for our

Maybe you should have actually read the specs you are claiming to
implemented before spending all that effort.