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

To: Jan Beulich <JBeulich@xxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
Subject: RE: [Xen-devel] Re: [PATCH][VTD] check BIOS settings before enabling interrupt remapping or x2apic
From: "Wei, Gang" <gang.wei@xxxxxxxxx>
Date: Wed, 6 Apr 2011 13:38:00 +0800
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Cc: "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Wei, Gang" <gang.wei@xxxxxxxxx>
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Thread-topic: [Xen-devel] Re: [PATCH][VTD] check BIOS settings before enabling interrupt remapping or x2apic
Jan Beulich wrote on 2011-04-05:
>>>> 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.)
> Jan

You are right. Take TXT into consideration, we should check the dmar table 
passed to acpi_parse_dmar(), and should not check the dmar_table directly.


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