[Xen-devel] Re: [PATCH] Fix xen hang on intel westmere-EP

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 23/08/2011 08:47, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> From: Keir Fraser
>> Sent: Tuesday, August 23, 2011 3:32 PM
>> 
>> On 23/08/2011 04:52, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
>> 
>>>> Further I'm opposed to introducing further instances of legacy brute- force
>>>> PCI
>>>> bus scans.
>>>> 
>>>> And I don't think you got something along these lines accepted into Linux,
>>>> did
>>>> you? It ought to be DMI based there, too.
>>> I don't know why you think using DMI is a better way? For BDF based way, we
>>> only need to know the device ID. But for DMI base way, I don't know which
>>> condition should be matched.
>>> 
>>> Actually, the best way to solve it is to enable the ACPI mode in Xen instead
>>> of in dom0. For enable ACPI, we need to write the value from
>> FADT.ACPI_ENABLE
>>> to SMI_CMD. After writing the value, the SMI ownership will be disable by
>> ACPI
>>> hardware and it also will disable some logic which is able to cause SMI. For
>>> example, the legacy USB circuit will be masked too. Because at this point,
>>> there have no need to use legacy usb emulation. This is also what linux
>>> upstream did. But I think it is too complicated to port this logic to xen.
>>> Anyway, if you have interesting, you can add this logic to xen and there
>>> have
>>> no need for this patch again.
>> 
>> It sounds like quite a good idea, and not very complicated at all. The main
>> concern would be potential other fall out from making the change.
>> 
> 
> This is indeed tricky though. This ACPI mode enable basically tells that Xen
> is
> ready to own ACPI hardware registers through ACPI SCI mode, instead of
> legacy SMI mode. However SCI itself requires some encoded ACPI information,
> such as routing and overlapping info, which depends on dom0. So Xen is not
> ready to handle SCI before dom0 boots.
> 
> On the other hand, Linux does this ACPI mode enable late until APs are
> ready to boot. Before that point there're some extra preparations completed
> already, such as DMI system check (which may disable ACPI), root namespace
> initialization, etc. I'm not sure whether those extra preparations can be all
> moved down to Xen (some of them access encoded content), or can be safely
> skipped in Xen (e.g. DMI check...)

That's a bit of a shame. Yes, sounds like quite a lot of pain.

 -- Keir

> Thanks
> Kevin



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