[Xen-devel] Skylake: VT-d and other error messages

[Eric Shelton <eshelton@xxxxxxxxx>]

Looking through the output of 'xl dmesg' on a Skylake system (i5-6600K), I found a number of error messages that I do not encounter on a Haswell-based system. I have tried two motherboards from different manufacturers, with pretty much the same results. Below are some of the unexpected messages:

Not enabling x2APIC (upon firmware request)

...

mwait-idle: does not run on family 6 model 94

...

[VT-D] iommu.c:875: iommu_fault_status: Primary Pending Fault

[VT-D] INTR-REMAP: Request device [0000:f0:1f.0] fault index 0, iommu reg = ffff82c000201000

(on motherboard 1) [VT-D] INTR-REMAP: reason 22 - Present field in the IRTE entry is clear

(on motherboard 2) [VT-D] INTR-REMAP: reason 25 - Blocked a compatibility format interrupt request

This leads to a few questions:

1) Is there some reason x2APIC should not be enabled on Skylake? What consequence, if any, is there not having x2APIC enabled?

2) Should mwait-idle be available on Skylake?

3) What about the IOMMU errors on Skylake - are they a concern?

Thank you,

Eric

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