On Tue, Jun 06, 2017 at 08:10:17PM +0200, Laszlo Ersek wrote: > On 06/05/17 18:02, Michael S. Tsirkin wrote: > > On Sat, Jun 03, 2017 at 09:36:23AM +0200, Laszlo Ersek wrote: > >> On 06/02/17 17:45, Laszlo Ersek wrote: > >> > >>> The patches can cause linker/loader breakage when old firmware is booted > >>> on new QEMU. However, that's no problem (it's nothing new), the next > >>> release of QEMU should bundle the new firmware binaries as always. > >> > >> Dave made a good point (which I should have realized myself, really!), > >> namely if you launch old fw on old qemu, then migrate the guest to a new > >> qemu and then reboot the guest on the target host, within the migrated > >> VM, things will break. > >> > >> So that makes this approach dead in the water. > >> > >> Possible mitigations I could think of: > >> - Make it machine type dependent. Complicated (we don't usually bind > >> ACPI generation to machine types) and wouldn't help existing devices. > >> - Let the firmware negotiate these extensions. Very complicated (new > >> fw-cfg files are needed for negotiation) and wouldn't help existing > >> devices. > > > > This last option *shouldn't* be complicated. If it is something's wrong. > > > > Maybe we made a mistake when we added etc/smi/*features*. > > > > It's not too late to move these to etc/*features* for new > > machine types if we want to and if you can do the firmware > > work. Then you'd just take out a bit and be done with it. > > > > I don't insist on doing the ACPI thing now but I do think > > infrastructure for negotiating extensions should be there. > > Different drivers in the firmware would need to negotiate different > questions / features with QEMU independently of each other. The "thing" > in OVMF that negotiates (and uses) the SMI broadcast is very-very > different and separate from the "thing" in OVMF that handles the ACPI > linker/loader script.
They both could call a common library. Also, we don't need separate fw cfg files - we could reserve ranges of bits in a single file. E.g. bits 0-31 - smi, 32-63 - tseg, etc. -- MST
