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Re: [Xen-devel] Xen, MCFG acpi table and E820 address map

 >>> On 04.09.13 at 18:24, Gordan Bobic <gordan@xxxxxxxxxx> wrote:
> On Wed, 4 Sep 2013 16:14:55 +0000, Santosh Jodh 
>  <Santosh.Jodh@xxxxxxxxxx> wrote:
>> -----Original Message-----
>> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
>> Sent: Wednesday, September 04, 2013 8:01 AM
>> To: Jan Beulich
>> Cc: Santosh Jodh; David Vrabel; xen-devel; Boris Ostrovsky
>> Subject: Re: [Xen-devel] Xen, MCFG acpi table and E820 address map
>> On Wed, Sep 04, 2013 at 10:16:26AM +0100, Jan Beulich wrote:
>>> >>> On 04.09.13 at 03:13, Santosh Jodh <Santosh.Jodh@xxxxxxxxxx> 
>>> wrote:
>>> > Xen will use information from MCFG acpi table to access PCIe
>>> > extended configuration space. However, Xen validates MCFG table by
>>> > making sure that the addresses specified in the MCFG table is
>>> > correctly marked as reserved in the E820 address map. If it is 
>>> not,
>>> > the MCFG table is ignored - thereby preventing Xen from accessing 
>>> PCIe extended configuration space.
>>> >
>>> > I recently came across a workstation class system that supports
>>> > VT-d. This system BIOS has a valid MCFG table. The BIOS does NOT
>>> > report the MCFG addresses as reserved in the E820 address map.
>>> > However, the addresses ARE claimed as reserved via the ACPI
>>> > motherboard resource devnode (PNP0C01) mechanism.
>> Could you tell me what machine this is? It would be good to know to
>> develop a patch against it.
>> [Santosh Jodh] Unfortunately, this is a new platform I cannot
>> disclose much about.
>  If this is pre-release/experimental hardware, isn't the
>  right thing to do to talk to the manufacturer and get them
>  to fix the BIOS so it exposes the correct e820 map in the
>  first place?

No. As said in an earlier reply, this is legitimate behavior that - as
shown - Linux can deal with. It's just the lack of the use of the
intended interface by the pv-ops kernel that gets in the way
here. In fact I have at least one system that also exhibits such
behavior; whether that's also a pre-release specific situation
(most of the systems I use for regular testing found their way
here by other than purchase) I can't tell, but it at least got me
to spot the Linux side solution and integrate it with Xen.


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