On 24/01/16 18:21, Thierry Laurion wrote:
> Hi devs!
>
> XEN devs:
> As per short discussion with ktemkin earlier in January in #xen:
>
> "ktemkin Jan 10, 2016 16:21:50
> This test patch did appear to make the system work, though:
> https://gist.github.com/ktemkin/0e81b93654ae800a5609
>
> ktemkin Jan 10, 2016 16:24:55
> Only real difference I see between that and the upstream behavior
> (besides limiting things to dom0 so things weren't accidentally passed
> through) is the call to disable_pmr on line 117 before aborting."
>
>
>
> Makes total sense to my early understanding, since it seems that it is
> said that vt-d engine gets disabled, but disable_pmr(iommu) function
> is not called to enforce.
>
> What do you think?

There is some confusion here.

"Unfortunately, quirks specific to the Clarkdale/Nehalem integrated
graphics device (IGD) do not function correctly with Xen's VT-d
implementation"

Either
1) There is a chipset errata which prevents it from functioning
correctly, or
2) Xen's VT-d code doesn't program the chip correctly.

Which is it?

If it is 1), then there is a very good case for quirking the affected
chipsets and unilaterally disabling them.  If it is 2), then the VT-d
code should be corrected.

~Andrew