Re: [Qemu-devel] [PATCH] acpi: change CPU container node _HID to compatible PNP0A05

[Igor Mammedov]

On Mon, 22 May 2017 14:01:15 +0300
Evgeny Yakovlev <address@hidden> wrote:

> On 22.05.2017 13:35, Igor Mammedov wrote:
> > On Mon, 22 May 2017 12:50:30 +0300
> > Evgeny Yakovlev <address@hidden> wrote:
> >  
> >> When running windows 2016 server guests we have encountered a problem
> >> with ACPI representation of CPU devices. This windows version contains a
> >> hidinterrupt.sys driver which looks for ACPI device node with _HID set
> >> to "ACPI0010" and "ACPI0011". ACPI0010 is also a valid id for CPU
> >> container device which qemu uses.
> >>
> >> hidinterrupt driver takes over (even though it fails) ACPI0010 node and
> >> thus hides its children -- the CPUs -- from the regular ACPI
> >> enumeration.  So there are no processors in the Windows device tree
> >> Device Manager or "!devnode 0 1" in the debugger.
> >>
> >> hidinterrupt.inf as shipped with Windows 2016 has both ACPI0011 and
> >> ACPI0010; the record for the latter is preceded with a comment "This Id
> >> is not to be used. It will be removed once everyone has stopped using
> >> it."  So I guess the typo was not in the driver but in the ACPI tables
> >> of some device(s) which the driver wanted to support despite the bug.
> >>
> >> For reference this is a known issue:
> >> https://bugzilla.redhat.com/show_bug.cgi?id=1377155#c31
> >>
> >> This change works around this problem by setting qemu CPU container ACPI
> >> _HID to compatible PNP0A05.  
> > I'd say NACK to it.
> > It's Windows server 2016 bug that violates spec and
> > it's been reported to them before RTM has been released.
> > So complain to Microsoft support and make them fix it.
> >
> > Meanwhile there is MS suggested workaround to fix issue,
> > one can use https://bugzilla.redhat.com/show_bug.cgi?id=1377155#c17
> >
> > Perhaps I should add workaround link as comment above line:
> >
> > aml_append(cpus_dev, aml_name_decl("_HID", aml_string("ACPI0010")));  
> 
> Thanks for replying!
> 
> Strictly speaking, this is not a Windows bug. Comment in INF file says 
> that they had to support a hardware device which erroneously picked this 
> ACPI HID.
in linux kernel we use device specific quirks to workaround broken hardware,
there is no point to break generic code for all hardware configurations
for the sake of one broken firmware.
So it's Windows problem that they prefer to violate spec and cannibalize
ACPI0010 for the sake of broken firmware. Open support case with Windows,
the more complains they get, the more chances that they'll fix it.

> I understand that this is not a qemu problem either. Then again other 
> emulators we've tested this on (VirtualBox, Parallels, HyperV) provide a 
> compatible ACPI configuration and don't trigger this conflict. If this 
we provide it, that's what '_CID' field is for, so OS that doesn't know
about ACPI0010 would be happy (any Windows prior Win10/2016)

> fix is not a big deal and does not affect anything negatively then maybe 
> we pay a relatively small price to improve compatibility with some guest 
> systems?
we plan to reuse this code for ARM in future and it might use
ACPI0010 container as per spec to describe modeled topology.
Hence no workaround in QEMU, just use MS suggested workaround
to remove wrong device binding in WS2016 until they actually
fix it.


> >> Signed-off-by: Evgeny Yakovlev <address@hidden>
> >> ---
> >>   hw/acpi/cpu.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
> >> index a233fe1..b93db40 100644
> >> --- a/hw/acpi/cpu.c
> >> +++ b/hw/acpi/cpu.c
> >> @@ -397,7 +397,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, 
> >> CPUHotplugFeatures opts,
> >>           Aml *rm_evt = aml_name("%s.%s", cphp_res_path, CPU_REMOVE_EVENT);
> >>           Aml *ej_evt = aml_name("%s.%s", cphp_res_path, CPU_EJECT_EVENT);
> >>   
> >> -        aml_append(cpus_dev, aml_name_decl("_HID", 
> >> aml_string("ACPI0010")));
> >> +        aml_append(cpus_dev, aml_name_decl("_HID", 
> >> aml_string("PNP0A05")));
> >>           aml_append(cpus_dev, aml_name_decl("_CID", 
> >> aml_eisaid("PNP0A05")));
> >>   
> >>           method = aml_method(CPU_NOTIFY_METHOD, 2, AML_NOTSERIALIZED);  
> 
>