Re: [Xen-devel] IOMMU initialization failure when using linux-as-bootloader

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/08/16 10:57, Sylvain Munaut wrote:
> Hello,
>
>
> I'm trying to use "linux as a bootloader", i.e. kexec into Xen 4.7 and
> I've been struggling for the past week. I've been able to debug and
> fix some issues on my own ( ELF header issue, invalid BDA entries,
> some kexec-tools bugs, ...) but I've been stuck on this one with no
> idea how to even debug it.
>
> Basically what I'm getting now is :
>
> (XEN) DMAR_IQA_REG = 47ad78002
> (XEN) DMAR_IQH_REG = 440
> (XEN) DMAR_IQT_REG = 20
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) queue invalidate wait descriptor was not executed
> (XEN) ****************************************
>
> If I try with iommu=off, then xen actually loads the dom0 kernel but
> it fails with various IO errors and not managing to access the drives,
> USB and so on. So obviously something is not quite initialized right,
> but I have no idea what.
>
> I should also not that kexec'ing into the dom0 kernel directly,
> without xen, works just fine.
>
> Does anyone have any clue what could be going on, or what I could do next ?
We gave a queued invalidation request to the IOMMU, and it didn't respond.

Given the position in the log, this is likely the very first time we 
have tried interacting with the IOMMU, and given the fact you used kexec 
to get here, it is likely that it is already set up from Linux's use.
It is probably something like we aren't resetting it, and either 
interacting with it in a mismatch between polled or interrupt mode, or 
that it has interrupts set up and they are going to an unexpected location.
> Below is the full xen serial console output. And you can also find a
> diff of a native (from grub) boot vs a kexec one :
> http://pastebin.com/M3X2ZvPx
>
> If you need more info, please ask, I can test or post more details if needed.
>
>
> Cheers,
>
>     Sylvain Munaut
>
>
>
>
> (XEN) Xen version 4.7.0 (whatever@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx)
> (gcc (Debian 4.9.2-10) 4.9.2) debug=n Fri Aug 26 09:07:38 UTC 2016
Please always  use a debug version of Xen to develop with.

~Andrew

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