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[Xen-devel] IOMMU Interrupt Remapping query

I am attempting to fix the kexec interactions with x2apic and iommu
functionality.  Part of this involves ensuring that all IOMMU
functionality is disabled, as the kdump kernels are not happy at having
their interrupts remapped without their knowledge.

I have introduced iommu_disable_x2apic_IR() onto the kexec path, but it
does not seem to actually disable interrupt remapping on Intel boxes
(Specifically the two Intel Nehalem boxes I am testing on).

Specifying iommu=no-intremap on the commandline causes everything to
work correctly, but leaving it out causes the kdump kernel to hang and
eventually reboot, as can be seen on the attached serial log.

The lines starting DBG: are extra debugging I have put in which shows
that the disable_IR() function is being called and writing to the registers.

This problem occurs with the XenServer version of 4.1.0 as well as on
xen-unstable at the moment.

Is there any hardware state which is not taken down by the disable
function, any subtle interactions which I have not taken account of?  I
have looked through the source and nothing pops out, but I am out of ideas.

Thanks in advance,

Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com

Attachment: andrewcoop-ohno-kdump-remap
Description: Text document

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