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[vfio-users] Intel 55x0 chipset problems with VT-d

This may relate to my query last week about passthrough with NVIDIA K420
on HP Z800, which is based on the Intel 5520 chipset.

I went looking for more details about chipset support and this is what
I've found:

The Intel datasheet[1] says VT-d is supported (see page 27, "Product

Intel issued a specification update[2] listing various errata/faults
that impact VT-d.  Some are only present in the first version of the
chipset (stepping B3) and fixed in the second version (stepping C2).

- looking at that list, is there anything that stands out that suggests
it will never work, either with the B3 or even the newer C2 version?

A Novel/SUSE Linux knowledgebase article[3] includes some of the
following comments:
- a message in the log (dmesg) should indicate if the chipset is buggy
- interrupt remapping should be disabled on systems with this hardware
- some vendors may issue a firmware update to fix the root cause
- passthrough can't be used with KVM on systems having this bug

Unfortunately, I found the warning appears in dmesg on the system in

[    0.022417] DMAR-IR: This system BIOS has enabled interrupt remapping
on a chipset that contains an erratum making that
feature unstable.  To maintain system stability
interrupt remapping is being disabled.  Please
contact your BIOS vendor for an update

If the system displays that in dmesg, why does qemu try to run at all?
Should the qemu command fail or give a warning too?

In a Citrix XenServer support article[4] on the same bug, it appears
that the BIOS update won't fix the issue, it will just provide a
workaround to stop people trying to enable interrupt remapping.  If I
understand correctly, passthrough just won't work on such systems.

Somebody has asked on the HP forum if they can change their motherboard
to go from the B3 to C2 chipset[5].  There is no response.

Looking on the HP download page for Z800, I found a new BIOS[6] but
nothing that appears to be a chipset firmware update (which is what the
Novell article suggests looking for).  The BIOS Revision History page
mentions latest Intel microcode though.

Has anybody else encountered issues like this?



3. https://www.novell.com/support/kb/doc.php?id=7014344
4. http://support.citrix.com/article/CTX136517

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