Hi, > > Well the crash of guest phys bits > host phys bits, should be easy to > > reproduce by booting a 65GB guest on a 64GB RAM + 2GB swap host with > > 36 host phys bits using the upstream qemu that forces the guest phys > > bits to 40. > > So you supply more RAM than host can address, and guest crashes?
Yep. The only reason we don't see this happening in practice is that it's probably next to impossible to find a machine which has (a) only 36 physical address lines and (b) allows to plug that much RAM. > Why are we worried about it? It's more a issue with pci ressources. In theory seabios/edk2 could go figure how big the physical address space is, then map 64bit pci bars as high as possible, thereby making stuff like etc/reserved-memory-end in fw_cfg unnecessary. But with qemu saying 40 phys bits are available even if they are not this approach isn't going to fly ... cheers, Gerd
