Re: [Xen-devel] Unable to boot Xen 4.8 with iommu=0

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Tian, Kevin
> Sent: Friday, February 17, 2017 11:35 AM
> > >>
> > >> Or wait - do you have the same issue if you use
> > >> "iommu=no,no-intremap"? In which case the problem would be
> > >> that "iommu=no" should clear more than just "iommu_enable", or
> > >> code checking iommu_intremap early (before iommu_setup()
> > >> manages to clear it in the case here) would need to made look at
> > >> both variables. Oddly enough acpi_parse_dmar() only bails if
> > >> both variables are clear, which suggests to me that
> > >> iommu_enable is intended to have two different meanings in
> > >> different contexts (master flag vs. controlling just DMA
> > >> remapping). Kevin, Feng - any thoughts here?
> > >
> > > iommu=no,no-intremap boots fine with "(XEN) Using APIC driver default"
> >
> > Thanks for confirming.
> >
> > Kevin, Feng, we now depend on your input regarding the intentions
> > with the two variables.
> >
> 
> Feng just left Intel. Let me take a look at code to understand the
> rationale behind.
> 

Jan, looks it's caused by your change back to 2012:

commit 7a8f6d0607a38c64506b4e8b473d955bf8e2a71f
Author: Jan Beulich <jbeulich@xxxxxxxx>
Date:   Fri Nov 2 17:15:30 2012 +0100

Before that iommu_enable was the master flag consistently. I'm still
trying to understand the background and you may help elaborate if
still something in your memory.

I agree we should stick to one meaning after clearing up above issue.

Given this commit is pretty old, I'm also curious why it's only reported
on 4.8. Tamas, did you succeed with iommu=0 pre 4.8, or 4.8 happens
to be the one upon which you first tried iommu=0 on a platform supporting
interrupt remapping?

Thanks
Kevin

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