[Pkg-xen-devel] Problems with PCI pass-through

[Thomas Schwinge]

Hello!

I'm having problems getting PCI pass-through to work.

This is on a AMD64 system, paravirtualized with xen-hypervisor-4.0-amd64
4.0.0-1~experimental.1, dom0: linux-image-2.6.32-5-xen-amd64 2.6.32-12.

From IRC, earlier today:

<tschwinge> waldi: Aren't the Debian xen domU-capable kernels supposed to
  contain the PCI frontend (needed for PCI pass-through)?  I'm getting:
  PCI: System does not support PCI
<tschwinge> waldi: ... both when using linux-image-2.6.32-3-686-bigmem
  and linux-image-2.6.32-5-xen-686 for the domU.
<tschwinge> Hrm.
  /boot/config-2.6.32-5-xen-686:CONFIG_XEN_PCIDEV_FRONTEND=y

So, yes for that one, and no for the 686-bigmem one -- which is also what
is said on
<http://wiki.xensource.com/xenwiki/XenKernelFeatures#head-9df801d47f748067dc67b71979905a00f9e3cef9>.

<tschwinge> Why doesn't think work then?
<tschwinge> xm pci-list-assignable-devices
<tschwinge> ... does show the device.
<tschwinge> If I start the domU, xm pci-list domU doesn show it, too.
<tschwinge> But then:
<tschwinge> kepler:~# dmesg | grep -i pci
<tschwinge> [    0.000000] Allocating PCI resources starting at 1c800000 (gap: 1c800000:e3800000)
<tschwinge> [    0.010467] PCI: setting up Xen PCI frontend stub
<tschwinge> [    0.020145] PCI: System does not support PCI
<tschwinge> [    0.020160] PCI: System does not support PCI
<tschwinge> [    0.204967] pcifront pci-0: Installing PCI frontend
<tschwinge> [    0.205093] pcifront pci-0: Creating PCI Frontend Bus 0000:00
<tschwinge> ... and lspci doesn't show anything.
<bwh^> That kernel seems... confused
<bwh^> OK, the two 'System does not support PCI' messages come from the
  PCIBIOS and PCI legacy probe code
<tschwinge> bwh^: So, any idea what might be wrong for me?
<bwh^> Not a lot
<bwh^> but those warnings can be ignored (and should really be improved)

In contrast to that:

<tschwinge> If I boot with the old pre-pvops 2.6.26-2-xen-686 kernel, I
  do see the PCI device with lspci: 00:00.7 Multimedia audio controller:
  Silicon Integrated Systems [SiS] AC'97 Sound Controller (rev a0)
<tschwinge> And dmesg is mostly the same:
<tschwinge> dmesg | grep -i pci
<tschwinge> [    0.000000] Allocating PCI resources starting at 20000000 (gap: 1d000000:e3000000)
<tschwinge> [    0.333116] PCI: Fatal: No config space access function found
<tschwinge> [    0.333133] PCI: setting up Xen PCI frontend stub
<tschwinge> [    0.353896] PCI: System does not support PCI
<tschwinge> [    0.353911] PCI: System does not support PCI
<tschwinge> [    0.401513] pcifront pci-0: Installing PCI frontend
<tschwinge> [    0.401609] pcifront pci-0: Creating PCI Frontend Bus 0000:00
<tschwinge> Yet, staying with that kernel won't be the solution.  :-)
<bwh^> tschwinge: No indeed

If I use the ``iommu=soft swiotlb=force'' switches as given on
<http://wiki.xensource.com/xenwiki/XenPCIpassthrough>, nothing changes,
apart from an additional ``PCI-DMA: Using software bounce buffering for
IO (SWIOTLB)'' line in the dmesg.

Any ideas?


Regards,
 Thomas
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