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[Xen-devel] RE: [PATCH][VTD] check BIOS settings before enabling interru

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-devel] RE: [PATCH][VTD] check BIOS settings before enabling interrupt remapping or x2apic
From: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
Date: Tue, 5 Apr 2011 11:13:58 -0700
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Cc: "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [PATCH][VTD] check BIOS settings before enabling interrupt remapping or x2apic
Not clear about the functional difference but I have moved the code inside of 
acpi_parse_dmar() in the latest patch.


-----Original Message-----
From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx] 
Sent: Tuesday, April 05, 2011 3:42 AM
To: Kay, Allen M
Cc: Cihula, Joseph; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser
Subject: Re: [PATCH][VTD] check BIOS settings before enabling interrupt 
remapping or x2apic

>>> On 29.03.11 at 19:58, "Kay, Allen M" <allen.m.kay@xxxxxxxxx> wrote:
> Check flags field in ACPI DMAR structure before enabling interrupt remapping 
> or x2apic.  This allows platform vendors to disable interrupt remapping or 
> x2apic features if on board BIOS does not support them.
> Signed-off-by: Allen Kay <allen.m.kay@xxxxxxxxx>

Taking a second look (while trying to merge this into our SLE11
code base), I think this

>@@ -761,7 +762,11 @@ out:
> int __init acpi_dmar_init(void)
> {
>+    struct acpi_table_dmar *dmar;
>     acpi_get_table(ACPI_SIG_DMAR, 0, &dmar_table);
>+    dmar = (struct acpi_table_dmar *) dmar_table;
>+    dmar_flags = dmar->flags;
>     return parse_dmar_table(acpi_parse_dmar);
> }

is wrong from a TXT perspective - the table obtained here must
only be used for the signature zapping activity, nothing else. All
decisions must be based upon what gets passed to
acpi_parse_dmar(). (This would at once reduce the size of
the change, since a cast struct acpi_table_dmar * is already
available there.)


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