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
