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Subject: Re: [virtio-dev] Memory sharing device

On Mon, Feb 11, 2019 at 6:49 AM Michael S. Tsirkin <mst@redhat.com> wrote:
On Mon, Feb 04, 2019 at 11:42:25PM -0800, Roman Kiryanov wrote:
> Hi Gerd,
> > virtio-gpu specifically needs that to support vulkan and opengl
> > extensions for coherent buffers, which must be allocated by the host gpu
> > driver. It's WIP still.
> the proposed spec says:
> +Shared memory regions MUST NOT be used to control the operation
> +of the device, nor to stream data; those should still be performed
> +using virtqueues.
> Is there a strong reason to prohibit using memory regions for control purposes?

That's in order to make virtio have portability implications, such that if
people see a virtio device in lspci they know there's
no lock-in, their guest can be moved between hypervisors
and will still work.

> Our long term goal is to have as few kernel drivers as possible and to move
> "drivers" into userspace. If we go with the virtqueues, is there
> general a purpose
> device/driver to talk between our host and guest to support custom hardware
> (with own blobs)?

The challenge is to answer the following question:
how to do this without losing the benefits of standartization?

Draft spec is incoming, but the basic idea is to standardize how to enumerate, discover, and operate (with high performance) such userspace drivers/devices; the basic operations would be standardized, and userspace drivers would be constructed out of the resulting primitives.

> Could you please advise if we can use something else to
> achieve this goal?

I am not sure what the goal is though. Blobs is a means I guess
or it should be :) E.g. is it about being able to iterate quickly?

Maybe you should look at vhost-user-gpu patches on qemu?
Would this address your need?
Acks for these patches would be a good thing.

Is this it:

https://patchwork.kernel.org/patch/10444089/ ?

I'll check it out and try to discuss. Is there a draft spec for it as well?


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