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Re: [Xen-devel] VT-d interrup remapping errata workaround



On 08/07/13 13:45, Malcolm Crossley wrote:
On 08/07/13 13:29, Jan Beulich wrote:
All,

just having spotted the backport of Linux commit 03bbcb2e I notice
a certain discrepancy with the Xen commit having the same purpose
as well as with the actual specification updates:

The Linux solution keys off of device IDs 3403 and 3406, as listed in
the specification update, but this way fails to cover the X58 chipset,
which has - under different numbers (62 and 69) - the same errata
(the Linux commit message also only mentions erratum 53 for the
55x0 chipsets, albeit I believe 47 is as much of an issue there as it is
for Xen).

The Xen solution keys off of ID 342e, with no explanation in the
commit description on where this association comes from.

I therefore wonder whether
- the Xen solution may have false positives
- the Linux solution would still have false negatives even after
   adding ID 3405

Jan

Hi Jan,

I have used the VT-d control PCI device which is common across X58/5520/5500

See page 233 http://www.intel.co.uk/content/dam/doc/datasheet/x58-express-chipset-datasheet.pdf
Whoops got the page number wrong it's page 223
and

page 255 http://www.intel.co.uk/content/dam/doc/datasheet/5520-5500-chipset-ioh-datasheet.pdf

It seems the Linux workaround only applies to the 5520 and 5500 chipsets.

The pci ID database suggests 0x342e will detect 7500 chipset (which does not have the interrupt remapping errata) but that chipset never reports revision 0x13 so the errata workaround will never be applied.

Also, if you check the devhide registers on page 318 of the 5520/5500 datasheet you can see the Device 0 (DMI port which the Linux uses for the PCI ID match) can be hidden from the PCI scan but device 20 function 0 can't be hidden (what Xen use's). You may find on a Dual IOH system that the DMI port for one of the IOH's is disabled.

Malcolm


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