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

>>> 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?


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