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

[Neil Horman <nhorman@xxxxxxxxxxxxx>]

On Mon, Jul 08, 2013 at 01:29:43PM +0100, 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
> 
Don Dutile noted that there was a problem he thought he noted with an X58
chipset that was simmilar to the one I fixed in the above commit.  I'm unabel to
track down an errata sheet for the X58 chipset, but if you have one and can
forward it to me I think it would be best (assuming that it has the same errata
that the 5500/5520 chipsets do), that we just add their pci device id's in to
the existing linux errata.

To answer your above questions, I'm not sure if the xen solution may offer false
positives, as I've not looked at the code.  The Linux solution may offer false
negatives, but only to the extent that this problem exists in chips not covered
by any errata sheet that I've found to date.  The errata sheet referencd in the
commit I have was exhaustive in the pci id's that it covered (which wsa limited
to 3403 and 3406).  If there are other chips that suffer from these errata, I
would like to see an errata sheet  that expressly identifies both the chip id's
and the problem.

Thanks
Neil

> Jan
> 
> 

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