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Re: [Xen-devel] Problems accessing passthrough PCI device

>>> On 13.11.14 at 14:29, <furryfuttock@xxxxxxxxx> wrote:
> I am having 2 major problems at the moment.
> 1.- Access to the PCI device from the PV will fail the second time I
> create it UNLESS I call xl pci-assignable-remove/pci-assignable-add
> between each creation. If I don't do this then all PCI accesses return
> -1. I get the same if I disable memory access in the PCI configuration
> register.
> 1.1.- Is this expected behaviour?

No. But did you verify the driver properly enables the device (i.e.
doesn't make assumptions on its state)? Also iirc some kernel
versions weren't properly resetting the device when coming back
from guest use, but without you stating the software versions
you're using that's just a remote possibility.

> 1.3.-  xl  dmesg  and  dmesg  in Dom0 do not show anything. I have set
> loglvl=all in the Xen command line.

"iommu=debug"? But given the symptoms above I don't really think
this is a problem with the IOMMU.

> 2.-  Whenever  I  perform a software reset on the PCI device (it is an
> Intel  82546  Ethernet  NIC) the hypervisor crashes. There is no oops,
> kernel  panic  or the like, just a crash. My development device has no
> serial port so I can't do much debugging.

A crash would imply you see something telling you it's a crash. If
you see nothing, I'd rather call it a hang or spontaneous reboot.
But even without serial port (assuming you can't even plug in a
serial port PCI card) there are ways to get at eventual crash output
(register+stack dump): For one, we've got USB debug port support.
This requires a special cable and there not being an (internal) hub in
between, but it's worth a consideration. And in the worst case,
"vga=keep" allows the hypervisor to continue printing to the screen
even post-boot. But that requires the video mode to not be changed
from the one Xen uses at boot (i.e. you should not use DRM's KMS,
and if you need to use X it would need to be configured to use the
frame buffer driver rather than any accelerating one).


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