On Thu, Jun 23, 2016 at 10:40:03AM +0200, Gerd Hoffmann wrote: > 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
Nah, x86 guests really need to go by _CRS. bios doesn't want to parse that so it can go by some fw cfg file instead. Going by phys bits won't work on old qemu so I don't believe it's practical. -- MST
