Re: [Qemu-devel] [PATCH 00/12] Allow EEH on spapr-pci-host-bridge devices

[David Gibson]

On Fri, Feb 26, 2016 at 10:31:51PM +1100, David Gibson wrote:
> For historical reasons, the spapr machine type has two PCI host bridge
> implementations: spapr-pci-host-bridge, and
> spapr-vfio-pci-host-bridge.  The latter was (duh) designed for VFIO
> devices, but later reworks mean it's not necessary for that, and VFIO
> can be used on the regular host bridge.
> 
> The only remaining difference is that EEH (Enhanced Error Handling -
> IBM's interface with similar purpose to AER) is only supported on the
> spapr-vfio-pci-host-bridge device.
> 
> This series corrects this, allowing EEH operations on the regular host
> bridge.  That allows the special VFIO host bridge (we leave a stub,
> for backwards compatibility).
> 
> EEH is only supported for VFIO devices, for the time being, and due to
> bugs in the kernel implementation, it is only usable when the host
> bridge only has devices from a single (host-side) IOMMU group
> ("Partitionable Endpoint", in IBM terminology).  That's an annoying
> limitation which we hope to lift someday, but it's no worse than now,
> since the spapr-vfio-pci-host-bridge only permits devices from a
> single IOMMU group in any case (although it doesn't properly enforce
> that).
> 
> I wrote these a while back, and I'm not sure why they got sidelined -
> I suspect I was looking for testing from Gavin Shan, not realising
> then that he was no longer working on EEH.  In any case, I'm hoping we
> can squeeze this change into 2.6, so we don't need to carry the broken
> spapr-vfio-pci-host-bridge device any longer.

Btw, Alexey.  Sorry, I know this will conflict with your vfio-ddw
patches.  However, from my brief glance at those, it looked like you
removed spapr-vfio-pci-host-bridge without properly fixing up EEH on
the regular host bridge, which I'd like to avoid.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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