On Fri, Jul 26, 2024 at 09:06:29AM +0100, David Woodhouse wrote:

That's great. You don't even need it to be per-vCPU if you let the
hypervisor write directly to the single physical location that's mapped
to userspace. It can do that before it even starts *running* the vCPUs
after migration. It's a whole lot simpler. 

It *seems* simpler, until you realize that there is no way
to change anything in the interface, there is no negotiation
between hypervisor and userspace. If I learned anything at all
in tens of years working on software, it's that it is
never done. So let's have userspace talk to the kernel
and have kernel talk to the devices, please. There's
no compelling reason to have this bypass here.

-- 
MST