Subject: Re: [PATCH 2/3] VFIO: VFIO_DEVICE_SET_ADDR_MAPPING command

From: Benjamin Herrenschmidt <[email-masked]>
Date: Wed, 20 Mar 2013 20:31:46 +0100

On Wed, 2013-03-20 at 12:48 -0600, Alex Williamson wrote:
> Perhaps my problem is that I don't have a clear picture of where
> you're
> going with this like I do for AER.  For AER we're starting with
> notification of an error, from that we build into how to retrieve the
> error information, and finally how to perform corrective action.  Each
> of these will be done through vifo-pci.
> 
> Here we're starting by registering a mapping that's really only useful
> to the vfio "accelerator" path, but we don't even have a hint of what
> the non-accelerated path is and how vfio is involved with it.  Thanks,

I'm surprised that you are building so much policy around AER ... can't
you just pass the raw stuff down to the guest and let the guest do it's
own corrective actions ?

As for EEH, I will let Gavin describe in more details what he is doing,
though I wouldn't be surprised if so far he doesn't have a
non-accelerated path :-) Which indeed makes things oddball, granted ...
at least for now. I *think* what Gavin's doing right now is a
pass-through to the host EEH directly in the kernel, so without a slow
path...

Gavin, it really boils down to that. In-kernel EEH for guests is a
KVMism that ends up not involving VFIO in any other way than
establishing the mapping, then arguably it could be done via a VM ioctl.

If there's more going through VFIO and shared state, then it should
probably go through VFIO-PCI.

Note (FYI) that EEH somewhat encompass AER... the EEH logic triggers on
AER errors as well and the error reports generated by the firmware
contain the AER register dump in addition to the bridge internal stuff.
IE. EEH encompass pretty much all sort of errors, correctable or not,
that happens on PCI. It adds a mechanism of "isolation" of domains on
first error (involving blocking MMIOs, DMAs and MSIs) which helps with
preventing propagation of bad data, and various recovery schemes.

Cheers,
Ben.