Re: [Xen-devel] [PATCH v6 7/8] AMD/IOMMU: allocate one device table per PCI segment

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.09.2019 18:30, Paul Durrant wrote:
>> -----Original Message-----
>> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan 
>> Beulich
>> Sent: 19 September 2019 14:25
>> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Suravee Suthikulpanit 
>> <suravee.suthikulpanit@xxxxxxx>
>> Subject: [Xen-devel] [PATCH v6 7/8] AMD/IOMMU: allocate one device table per 
>> PCI segment
>>
>> Having a single device table for all segments can't possibly be right.
> 
> The copy of the spec. I have says (on page 253: Fixed-Length IVHD
> Blocks) that IVHD entries must have a segment group of 0, so can't
> the code just require iommu->seg == 0?

The wording in my version is "At this time, only PCI Segment Group 0 is
supported." This suggests to me that it is not a good idea to have logic
baked in that depends on this remaining true. I realize though that there
are more places than just this one where we (have to) assume segment 0
(all in iommu_acpi.c, and all marked with an XXX comment).

Jan

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