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

[Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>]

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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