On Thu, 12 Mar 2020 20:48:48 +0200 Liran Alon <liran.a...@oracle.com> wrote:
> On 12/03/2020 18:35, Igor Mammedov wrote: > > On Thu, 12 Mar 2020 14:55:50 +0200 > > Liran Alon <liran.a...@oracle.com> wrote: > > > >> On 12/03/2020 14:19, Michael S. Tsirkin wrote: > >>> On Thu, Mar 12, 2020 at 01:30:01PM +0200, Liran Alon wrote: > >>>> On 12/03/2020 8:12, Michael S. Tsirkin wrote: > >>>>> On Thu, Mar 12, 2020 at 01:20:02AM +0200, Liran Alon wrote: > >>>>>> But this is just a good practice in general and in the past it was > >>>>>> said by > >>>>>> maintainers that this is one of the main reasons that ACPI and SMBIOS > >>>>>> generation have moved from SeaBIOS to QEMU. > >>>>> I think a flag to disable this might make sense though. For example, > >>>>> some guests might behave differently and get broken. > >>>> Right. That's why I think it's a good practice to have this flag and tie > >>>> it > >>>> to machine-type. > >>> Tying things to the machine type is not what I had in mind. > >>> A separate flag would also be helpful so users can tweak this > >>> for new machine types, too. > >> I think it's unnecessary, given how common WAET ACPI table is exposed by > >> default by other hypervisors. > >> > >> But if you insist, I can add such flag on a separate commit in v2... > >> Where do you want to have such flag? It cannot be a property of some > >> qdev object. > >> So you want to add a new QEMU_OPTION_no_weat in vl.c? > > If it doesn't break any windows guests we probably don't need an option. > > Can you test if old guests are booting fine with new table, to confirm > > that it's fine? (starting with XPsp3) > > Old guests boot fine with the new WAET table. > We are running with this table in production for many years with many > Windows XP guests (and much more esoteric guests) > > Just to verify, I've just now run it with a WinXP SP3 VM and it works > just fine. > So should I remove the flag completely or remain with the current > functionality I have that makes sure WAET is only exposed on new > machine-types? In this case I'd drop flag. > > -Liran > > >>>> Guest-visible changes shouldn't be exposed to old machine-types. > >>> Well almost any change in qemu is guest visible to some level. > >>> Even optimizations are guest visible. > >>> We made changes in ACPI without versioning in the past but I'm not > >>> opposed to versioning here. However in that case pls do add a bit > >>> of documentation about why this is done here. > >> I remember that maintainers have explicitly specified that ACPI/SMBIOS > >> should not be changed between machine-types. > >> This have been one of the reasons to move ACPI/SMBIOS generation from > >> SeaBIOS to QEMU control. > >> > >> What can of documentation you want me to add and where? > >> The only thing I can say is that I tie it to machine-type because I do > >> not think a given machine-type should suddenly change BIOS exposed info > >> to guest. > >> But that's kinda generic. I haven't found similar documentation in other > >> ACPI-disable flags to copy from (E.g. do_not_add_smb_acpi). > >> > >>> What I am asking about is whether we need a flag to disable > >>> this as part of the stable interface. > >> I personally think not. But if you think otherwise, can you provide > >> guidance of where you suggest to add this flag? > >> As the only place I see fit is adding a new QEMU_OPTION_no_weat. >
