Re: [Xen-devel] [PATCH 2/6] xl: Add commands for hiding and unhiding pcie passthrough devices

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Jul 18, 2017 at 02:38:14PM +0100, Wei Liu wrote:
> On Fri, Jul 07, 2017 at 10:00:01AM -0400, Konrad Rzeszutek Wilk wrote:
> > > 
> > > 1. PV PCI passthrough is done via pciback, which means the physical
> > >    device is assigned to the driver domain. All events to / from the
> > >    guest / device are handled by the driver domain -- which includes
> > >    the AER error you're trying to handle.
> > > 
> > > 2. HVM PCI passthrough is done via QEMU, but you also need to pre-assign
> > >    the device to the driver domain in which QEMU runs. All events are only
> > >    visible to the driver domain.
> > > 
> > > Yes, a guest is going to be always killable by Dom0 (the toolstack
> > > domain), even if some devices of the guest are handled by a driver
> > > domain.
> > > 
> > > But Dom0 now can't see the AER event so it won't be able to issue the
> > > "kill" or whatever action you want it to do. Is this not the case? Do
> > 
> > It can. That is how it works right now - the AER errors are sent to the
> > PCIe bridge which is a device driver in domain0. Then the kernel
> > sends it to pciback (which owns the device) to deal with.
> > 
> 
> So pciback will have to run in Dom0?

You need a kernel piece to deal with AER (as it is an normal interrupt to
the PCIe bridge and the PCIe bridge picks this up and does its thing).

The AER mechanism (in Linux) then walks through all the devices underneath
the PCIe bridge and gives it options to do things - and in case of pciback
we can do the right thing.

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