On 28/11/15 20:46, Eric Shelton wrote: > 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?
In this case, the firmware has set the x2apic opt-out bit in the DMAR table, indicating that Xen should not use x2apic. You might find an option in your BIOS to undo this; there have been enough errata in the past in this area that I would expect it to be a tweakable. x2apic is the extension to xapic, which permits more than 255 cpus. So long as you don't have that many, there isn't a specific problem with missing x2apic mode. > 2) Should mwait-idle be available on Skylake? We probably need to resync the mwait driver with Linux. It is whitelisted on known cpu model numbers. > 3) What about the IOMMU errors on Skylake - are they a concern? Yes. In both cases, PCI device f0:1f.0 is misconfigured or misbehaving. On motherboard 1, it is delivering an interrupt for which no remapping entry has been set up. On motherboard 2, it is delivering an compatibility-format interrupt, as opposed to a remapable-format interrupt. For motherboard 2, Xen should disallow such a configuration. Either interrupt remapping is enabled and all devices should be configured to issue remmapable interrupts, or interrupt remapping is disabled and everything should be configured to issue compatibility-format interrupts. Either way, diagnosing the problem here starts with identifying what f0:1f.0 is. ~Andrew
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