On 06/01/17 14:25, Laszlo Ersek wrote: > In QEMU, we could tie both of these extensions to new machine types. > > The result would be: > > firmware QEMU QEMU machine type result > -------- ---- ----------------- ----------------------------------- > old new old allocate blobs under 4GB > old new new breakage, but that's OK, we can > require refreshed firmware for > new machine types > new old old allocate blobs under 4GB > new new old allocate blobs under 4GB > new new new allocate blobs from 64-bit space
I think the situation is easier than this. We don't have to tie the extensions to machine types. The reason is that old firmware is allowed to fail on new QEMU (regardless of machine type). Example: the WRITE_POINTER command, originally introduced for VMGENID. If you run a SeaBIOS binary without WRITE_POINTER support, in a QEMU VM with "-device vmgenid", the device will not work. And QEMU doesn't try to prevent that by binding vmgenid to machine types. Instead, QEMU bundled a SeaBIOS binary with WRITE_POINTER support, for the release that introduced VMGENID. (There's no reason for not bundling OVMF and ArmVirtQemu binaries with QEMU releases now. Gerd already has a build service up and running, at <http://www.kraxel.org/repos/>.) The scenario that we *should* avoid is new firmware failing on old QEMU. And this patch is actually that case, because the new fw would allocate blobs with such 8-byte addresses that might not fit into 32-bit blob fields. So, the extensions are necessary, but tying them to machine types isn't. firmware QEMU result -------- ---- ------------------------------------------------------ old new breakage, but that's OK; we can require refreshed firmware for new QEMU releases new old allocate blobs under 4GB (alloc zone extension is necessary) new new allocate blobs from any address range Thanks Laszlo _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
