Re: [Qemu-devel] VFIO PCIe Extended Capabilities

[Alex Williamson]

On Tue, 19 Jul 2016 11:22:29 -0600
Alex Williamson <address@hidden> wrote:

> On Tue, 19 Jul 2016 17:12:45 +0000
> Spenser Gilliland <address@hidden> wrote:
> 
> > Hi,
> > 
> > I noticed your patches "vfio: add pcie extended capability support" and 
> > "vfio/pci: Hide SR-IOV capability" have gone into qemu mainline.  These 
> > look really good, and thanks so much for doing these.
> > 
> > I was wondering if there were any side effects to removing the 
> > pci_bus_is_express check on line 1776 of hw/vfio/pci.c .
> > 
> >     /* Only add extended caps if we have them and the guest can see them */
> > -   if (!pci_is_express(pdev) || !pci_bus_is_express(pdev->bus) ||
> > +  if (!pci_is_express(pdev) ||
> >         !pci_get_long(pdev->config + PCI_CONFIG_SPACE_SIZE)) {
> >         return 0;
> >     }
> > 
> > I'm asking because it looks like the defaults for libvirt/OpenStack are to 
> > create a "hostdev" stanza in the libvirt xml to define this pass through 
> > condition.  However, it also appears that the "hostdev" stanza only 
> > supports pci-bridge bus connections.  Thus, it's not easily possible to use 
> > this patch in a libvirt/OpenStack environment as the bus is technically a 
> > non-express bus.  It looks like adding PCIe bus support to 
> > libvirt/OpenStack may be a lot more effort than a simple workaround here.
> > 
> > I have tested this on my local system and it does work as intended for my 
> > use case.  The following is from an OpenStack VM and shows that the 0x340 
> > extended configuration space is passed through correctly.  I've also done 
> > testing which uses this space and the results are positive.  
> 
> If the bus is not express then extended capabilities on the device
> should not be accessible, this would be a QEMU bug for allowing it.
> Cc'ing Marcel for that.  Thanks,

In fact, I've tried to fix this multiple times:

https://lists.nongnu.org/archive/html/qemu-devel/2015-10/msg05384.html
https://lists.nongnu.org/archive/html/qemu-devel/2015-11/msg02422.html
https://lists.nongnu.org/archive/html/qemu-devel/2016-01/msg03259.html

Yet the patch remains unapplied :(