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Re: [Xen-devel] [PATCH v2 3/4] x86/vtd: introduce a PVH implementation of iommu_inclusive_mapping

On Tue, Aug 22, 2017 at 06:31:27AM -0600, Jan Beulich wrote:
> >>> On 11.08.17 at 18:43, <roger.pau@xxxxxxxxxx> wrote:
> > On certain Intel systems, as far as I can tell almost all pre-Haswell ones,
> > trying to boot a PVH Dom0 will freeze the box completely, up to the point 
> > that
> > not even the watchdog works. The freeze happens exactly when enabling the 
> > DMA
> > remapping in the IOMMU, the last line seen is:
> > 
> > (XEN) [VT-D]iommu_enable_translation: iommu->reg = ffff82c00021b000
> > 
> > In order to workaround this (which seems to be a lack of proper RMRR 
> > entries,
> > plus the IOMMU being unable to generate faults and freezing the entire 
> > system)
> > add a PVH specific implementation of iommu_inclusive_mapping, that maps
> > non-RAM, non-unusable regions into Dom0 p2m. Note that care is taken to not 
> > map
> > device MMIO regions that Xen is emulating, like the local APIC or the IO 
> > APIC.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> I don't mean to object to the patch, but it certainly would be helpful
> to understand the behavior a little better, in particular also to
> perhaps be able to derive what RMRRs are missing (which could
> then be added via command line option instead of this all-or-norhing
> approach). Kevin, could you perhaps help here?

I tied that, but since the system freezes completely I have no idea
what's missing. It's quite clear to me that it's related to the IOMMU
and it's inability to properly generate a fault, but further than that
I have no other clue.


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