Re: [Qemu-devel] Commit 77af8a2b95b79699de650965d5228772743efe84 breaks Windows 2000 support

[Igor Mammedov]

On Wed, 26 Jul 2017 15:10:40 +0200
Paolo Bonzini <address@hidden> wrote:

> On 26/07/2017 15:08, Igor Mammedov wrote:
> > On Tue, 25 Jul 2017 18:23:22 +0200
> > Paolo Bonzini <address@hidden> wrote:
> >   
> >> On 25/07/2017 18:14, Laszlo Ersek wrote:  
> >>>   "No regressions became apparent in tests with a range of Windows
> >>>    (XP-10)"
> >>>
> >>> In theory, w2k falls within that range.    
> >>
> >> Nope, Windows 2000 is like NT 5.0, XP is like NT 5.1. :(
> >>
> >> One possibility is to fix it in SeaBIOS instead: if you get a 2.0 FADT
> >> and an XSDT and no RSDT, it can build an RSDT and a 1.0 FADT itself,
> >> patching the RSDT to point to it.
> >>
> >> It's a hack, but it's the only place I see to make it "just work".  And
> >> it could be extended nicely in the future.
> >>
> >> All QEMU would have to do is to provide an XSDT _instead_ of an RSDT.  
> > I'd support it, however it would break migrated guests with old BIOS
> > image in RAM on reboot.  
> 
> Why?  Shouldn't the old ACPI tables get migrated together with the old
> BIOS?  Or are they rebuilt after reset?
they are rebuild on reset, but I've been wrong
Looking at SeaBIOS something similar to your suggestion also should work,
 if 
    RsdpAddr = find_acpi_rsdp();
 fails, current SeaBIOS falls back to its own ACPI tables.

but it seems that we don't even need to go to that extent,
all user have to do is to use "-no-acpi" CLI option with QEMU
for any SeaBIOS to fallback to embedded legacy ACPI tables.

Maybe we should just fix wiki
  http://wiki.qemu.org/Windows2000
to recommend using '-no-acpi' option when running w2k and
leave PC machine at rev3 and mention it in release notes.

Opinions?

> Paolo
> 
> > Legacy users have an option to build SeaBIOS without ACPI from QEMU
> > support by turning off CONFIG_FW_ROMFILE_LOAD (or use old SeaBIOS)
> > which leads to using legacy tables included in SeaBIOS.
> > Then mgmt layer above libvirt which knows what guest OS it's
> > going to run can pick legacy BIOS image for it.
> > 
> > But the testing issue will still stay as normally it's not tested
> > path.
> > 
> > PS:
> > For now we are going to revert PC machine to rev1 and leave q35 at rev3
> > as Michael suggested to keep both w2k and macos happy.
> >   
> >>
> >> Paolo
> >>  
> >>> In practice, it is impossible to
> >>> test *all* Windows versions against ACPI generator changes, even if you
> >>> try to be thorough (which Phil was). One might not even *know about*
> >>> "all" Windows versions. So people using w2k and similar should
> >>> co-maintain the ACPI stuff and report back with testing on the fly;
> >>> otherwise regressions are impossible to avoid.    
> >>  
> >   
>