[virtio-dev] Re: [virtio-comment] [PATCH 00/11] Introduce transitional mmr pci device

Michael S. Tsirkin
2023-04-03T20:04:19Z

On Mon, Apr 03, 2023 at 07:48:56PM +0000, Parav Pandit wrote:
> > OK but supporting them with a passthrough driver such as vfio does not seem
> > that important.
> Not sure on what basis you assert it.
> I clarified in the cover letter that these are the user level requirements to support transitional and non-transitional devices both via single vfio subsystem.

And what is so wrong with vdpa? Really I don't see how the virtio spec
needs to accomodate specific partitioning between linux modules, be it
vdpa or vfio. Way beyond the scope of the driver.

But anyway, my main
point is about DMA. On the one hand you are asking for a VQ based
management interface because it saves money. On the other you are
saying DMA operations take extremely long to the point where they are
unusable in the boot sequence.
So what is it? Was admin vq a mistake and we should do memory mapped?
I know Jason really wanted that, and it makes a bunch of things
easier. Or is legacy emulation doable over a vq and latency is not
a concern, and the real reason is because it makes you push out
a host driver with a bit less effort?

I just do not see how these claims do not contradict each other.

--
MST