Re: [virtio-dev] [RFC QEMU] docs: vhost-user: Add custom memory mapping support

[Viresh Kumar <viresh.kumar@xxxxxxxxxx>]

On 01-03-23, 12:29, Stefan Hajnoczi wrote:
> What is the advantage over defining separate messages? Separate messages
> are cleaner and more typesafe.

I thought we wanted to keep single message for one kind of functionality, which
is mmap related quirks here. And so it would be better if we can reuse the same
for next hypervisor which may need this.

The value parameter is not fixed and is hypervisor specific, for Xen this is the
domain id, for others it may mean something else.

> I don't have a concrete example, but was thinking of a guest that shares
> memory with other guests (like the experimental virtio-vhost-user
> device). Maybe there would be a scenario where some memory belongs to
> one domain and some belongs to another (but has been mapped into the
> first domain), and the vhost-user back-end needs to access both.

These look tricky (and real) and I am not sure how we would want to handle
these. Maybe wait until we have a real use-case ?

> The other thing that comes to mind is that the spec must clearly state
> which mmaps are affected by the Xen domain information. For example,
> just mem table memory regions and not the
> VHOST_USER_PROTOCOL_F_LOG_SHMFD feature?

Maybe we can mention that only the mmap's performed via /dev/xen/privcmd and
/dev/xen/gntdev files are affected by this ?

-- 
viresh