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

To:	Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] ACPI-Tables corrupted?
From:	Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date:	Wed, 28 Jul 2010 13:26:46 +0200
Cc:	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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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?

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@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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