> On 12/05/2017 01:55, Xu, Anthony wrote: > > Hi Paolo, > > > > In KVM mode, seems A20 is ignored. > > Do you see any potential issue here? > > No; recent processors don't have A20 at all.
I mean A20 in guest, not A20 in host. Guest is running on old platform, it tries to control A20 through port 92 like what SeaBios does. QEMU/KVM does handle port 92 access to set correct env->a20_mask, but QEMU/KVM ignores A20 status when handling guest memory access. Since QEMU/KVM works well with SeaBios, does that imply SeaBios doesn't generate address larger than 0x100000 in real mode? If that's the case, QEMU/TCG should work with SeaBios even with ignoring A20. During SeaBios boot, there are >350 port 92 access, if we don't need to handle A20, we can make A20 configurable in Seabios, It may reduce SeaBios boot time. Anthony
