On 13/03/2018 19:49, Eduardo Habkost wrote: >>> >>> Exactly, in other words these two options are part of the guest >>> ABI, and QEMU promises to never make the guest ABI depend on the >>> host hardware unless you're using "-cpu host". >> >> This is not entirely true; while MAXPHYADDR is constant downstream >> unless using "-cpu host", in practice that behavior is wrong and a guest >> could misbehave if passed a MAXPHYADDR that is different from the host's. >> >> I think this is the same, and management software will have to live with it. > > I think they are very far from being equivalent. Right, I only meant to say that guest ABI actually does depend on the host hardware, even outside of "-cpu host". > But if you tell the guest the wrong C-bit location, guests are > likely to rely on it and break. Migration between hosts with > different C-bit locations won't work, will it? It won't---but as long as the destination hosts fails fast when the C-bit location is wrong, it's okay. What matters is that we don't run guest code with the wrong C bit, as you noted. Paolo
