On 08/06/2017 18:10, Laszlo Ersek wrote: > When the guest writes value 0xffff to this register, the value that can be > read back is that of "mch.extended-tseg-mbytes" -- unless it remains > 0xffff. The guest is required to write 0xffff first (as opposed to a > read-only register) because PCI config space is generally not cleared on > QEMU reset, and after S3 resume or reboot, new guest firmware running on > old QEMU could read a guest OS-injected value from this register.
I guess that's also a reason not to make it readonly (that is, it would require some firmware code anyway to test for "readonlyness" and distinguish old machine types from new)? Thanks, Paolo
