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Re: [Xen-devel] ACPI-Tables corrupted?

To: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] ACPI-Tables corrupted?
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 28 Jul 2010 12:39:24 +0100
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On 28/07/2010 12:26, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

> On 07/28/2010 12:03 PM, Keir Fraser wrote:
>> On 28/07/2010 10:38, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>  wrote:
>>> As you can see, the DMAR eye-catcher is replaced by blanks!
>>> This leads to a programmed panic in the crash kernel later in case of a
>>> panic in dom0...
>>> Any ideas?
>>> BTW: seen in unstable AND 4.0
>> Look at the tail of xen/drivers/passthrough/vtd/dmar.c: Xen *always*
>> *unconditionally* trashes the DMAR so that dom0 will not parse it.
>> Presumably bad stuff would happen if it did.
> As Dom0 is a pv-kernel, it should be able to ignore this entry.
> The crash kernel OTOH should not panic due to the trashed entry!
> What is the correct solution here?

Could provide a cmdline option to not nobble the DMAR?

> The crash kernel expects a valid DMAR entry, as following code in
> enable_IR_x2apic() suggests:

I don't know what that function does, nor how the error path below depends
on DMAR. DMAR isn't mentioned in the below code.


>          /* IR is required if there is APIC ID > 255 even when running
>           * under KVM
>           */
>          if (max_physical_apicid > 255 || !kvm_para_available()) {
>              if (max_physical_apicid > 255) {
>                  pr_warning("NTR enable_IR_x2apic max_physical_apicid >
> 255\n");
>              }
>              if (!kvm_para_available()) {
>                  pr_warning("NTR enable_IR_x2apic !kvm_para_available()\n");
>              }
>              goto nox2apic;
>          }
> (kernel is from Novell SLES11 SP1, the pr_warnings were added to
> find the error path - it was the !kvm_para_available())
> Looking closer to the code rises some doubts about correctness. The comment
> at top seems not to be reflected by the following if...
> Juergen

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