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Re: [Xen-devel] pre Sandy bridge IOMMU support (gm45)

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"

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.

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