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

[Sylvain Munaut <s.munaut@xxxxxxxxxxxxxxxxxxxx>]

Hi Jan,


> I think this is reasonable, despite it certainly being unexpected for
> the BIOS to turn such on when not putting the system into x2APIC
> mode.

It seems that linux doesn't use x2APIC because the BIOS explicitly
"opts out" of it :

"DMAR-IR: x2apic is disabled because BIOS sets x2apic opt out bit."


> Considering you're not talking about a BIOS here, may I
> nevertheless ask why it's not instead Linux/kexec which get fixed
> to not leave these features enabled before handing off control?

I think both should be done.

Xen should tolerate that case and not assume that if it's enabled it's
been enabled by Xen.
Especially since that "pre-cleanup" already exists in one path and not
the other.

But the kernel should definitely clean up as much as possible after
itself before reboot.
I've actually been looking into that this morning but didn't come up
with a solution yet.

The Xen case was easy because I just had to copy the missing calls
from one codepath to the other, for the linux path I'm still looking
how & where to do that. If I'm still no closer to an answer by
tomorrow, I'll ask on the kexec mailing list if anyone has any
suggestion.


Cheers,

    Sylvain

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