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Re: [Qemu-devel] Commit 77af8a2b95b79699de650965d5228772743efe84 breaks

From: Paolo Bonzini
Subject: Re: [Qemu-devel] Commit 77af8a2b95b79699de650965d5228772743efe84 breaks Windows 2000 support
Date: Wed, 26 Jul 2017 15:33:37 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 26/07/2017 15:30, Igor Mammedov wrote:
> 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

Hmm so we need this plus keeping old machine types fixed to rev1 and
RSDT.  Diffstat will get worse. :)


> 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.    

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