Re: IOMMU Interrupt Remapping query

[Keir Fraser <keir.xen@gmail.com>]

On 06/06/2011 15:32, "Andrew Cooper" <andrew.cooper3@citrix.com> wrote:

> 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.

Should have attached your patch as well. Noone else can know with certainty
where you put your debugging, and noone else is going to want to help debug
your code if they can't even see it. :-)

Also a good idea to Cc a likely person who can help (i.e., someone who wrote
the code that you are querying). 'hg annotate' is useful for this -- in this
case I am adding Weidong Han to the cc list.

On the bright side, this must have been got working for S3 suspend/resume to
work properly (indeed that's what the disable code was originally added
for). So it can't be an insurmountable problem.

 -- Keir

> 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,