On 2019/11/25 上午8:09, Jason Gunthorpe wrote:
On Sun, Nov 24, 2019 at 10:51:24PM +0800, Tiwei Bie wrote:
You removed JasonW's other reply in above quote. He said it clearly
that we do want/need to assign parts of device BAR to the VM.
Generally we don't look at patches based on stuff that isn't in them.
The hardware is ready, and it's something really necessary (for
the performance). It was planned to be added immediately after
current series. If you want, it certainly can be included right now.
I don't think it makes a significant difference, there are enough
reasons already that this does not belong in vfio. Both Greg and I
already were very against using mdev as an alterative to the driver
core.
Don't get us wrong, in v13 this is what Greg said [1].
"
Also, see the other conversations we are having about a "virtual" bus
and devices. I do not want to have two different ways of doing the same
thing in the kernel at the same time please. Please work together with
the Intel developers to solve this in a unified way, as you both
need/want the same thing here.
Neither this, nor the other proposal can be accepted until you all agree
on the design and implementation.
"
[1] https://lkml.org/lkml/2019/11/18/521
IIUC, your point is to suggest us invent new DMA API for userspace to
use instead of leveraging VFIO's well defined DMA API. Even if we don't
use VFIO at all, I would imagine it could be very VFIO-like (e.g. caps
for BAR + container/group for DMA) eventually.
None of the other user dma subsystems seem to have the problems you
are imagining here. Perhaps you should try it first?
Actually VFIO DMA API wasn't used at the beginning of vhost-mdev. But
after the discussion in upstream during the RFC stage since the last
year, the conclusion is that leveraging VFIO's existing DMA API would
be the better choice and then vhost-mdev switched to that direction.
Well, unfortunately, I think that discussion may have led you
wrong. Do you have a link? Did you post an ICF driver that didn't use vfio?
Why do you think the driver posted in [2] use vfio?
[2] https://lkml.org/lkml/2019/11/21/479
Thanks
Jason
