Re: [Qemu-devel] [PATCH v3 0/4] Introduce the microvm machine type

[Paolo Bonzini]

On 25/07/19 16:46, Michael S. Tsirkin wrote:
> Actually, I think I have a better idea.
> At the moment we just get an exit on these reads and return all-ones.
> Yes, in theory there could be a UR bit set in a bunch of
> registers but in practice no one cares about these,
> and I don't think we implement them.
> So how about mapping a single page, read-only, and filling it
> with all-ones?

Yes, that's nice indeed. :)  But it does have some cost, in terms of
either number of VMAs or QEMU RSS since the MMCONFIG area is large.

What breaks if we return all zeroes?  Zero is not a valid vendor ID.

Paolo