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

[Michael S. Tsirkin]

On Thu, Jul 25, 2019 at 05:35:01PM +0200, Paolo Bonzini wrote:
> 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

It isn't but that's not what baremetal does. So there's some risk
there ...

Why is all zeroes better? We still need to map it, right?

-- 
MST