From mboxrd@z Thu Jan  1 00:00:00 1970
From: Juergen Gross <juergen.gross@ts.fujitsu.com>
Subject: Re: ACPI-Tables corrupted?
Date: Wed, 28 Jul 2010 13:26:46 +0200
Message-ID: <4C5013F6.3090005@ts.fujitsu.com>
References: <C875BF08.1BD21%keir.fraser@eu.citrix.com>
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On 07/28/2010 12:03 PM, Keir Fraser wrote:
> On 28/07/2010 10:38, "Juergen Gross"<juergen.gross@ts.fujitsu.com>  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?

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

         /* 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 2.6.32.12 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

-- 
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@ts.fujitsu.com
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html