Re: [Xen-devel] SR-IOV problems - HVM cannot access network

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 2 Mar 2011, David white wrote:
> 
> On Wed, 2 Mar 2011, Stefano Stabellini wrote:
> 
> > On Wed, 2 Mar 2011, David White wrote:
> > > Thanks for your help so far.
> > >
> > > Ubuntu Maverick is only running in the guest HVM domains.
> > >
> > > I have two boards I am testing with, both with Intel 5520 chipset.  I'm 
> > > using
> > > two 82576 nics from two different vendors, one attached to either board.  
> > > Both
> > > systems have AMI bios.  One system (call it systemA) has bios options for 
> > > both
> > > VT-d and SR-IOV, and both are enabled, as is I/OAT.  The other system 
> > > (systemB)
> > > has bios options for VT-d and "Coherency support" (which seemed to help me
> > > enumerate the VFs), and both are enabled (no mention of I/OAT).
> > >
> > > SystemA runs Debian Squeeze and the xen kernel, vmm and tools from that 
> > > distro.
> > > SystemB runs Fedora14 with the well-known "jeremy" kernel
> > > (http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=shortlog;h=xen/stable-2.6.32.x),
> > > and xen-4.0.1 hypervisor built from source (unaltered).
> > >
> > > Both systems are experiencing the same behavior.
> > >
> > > attached are dom0 and hvm ethregs output for the VF using '-o -m'
> > > flags.  This one was taken from the Debian host ("systemA")
> >
> > could you please try adding
> >
> > acpi=0
> >
> > in your VM config file?
> >
> 
> Hm, ok that seemed to do the trick, as far as getting the VFs up on the 
> network.
> 

Thank you very much for testing this, it proves that the recent problems
with VF passthrough and HVM Linux guests are the same issue reported
here:

http://marc.info/?l=xen-devel&m=129847075105008&w=2

and here:

http://marc.info/?l=xen-devel&m=129891005422870&w=2


> Is this by design or is it a workaround? Must I sacrifice acpi in my guest to
> enable sr-iov?  Does this come with a cost to I/O performance, since the guest
> isn't using MSI?
 
It is just a workaround.
It shouldn't cost you any performance at all, but you won't be able to
hot-plug or hot-unplug PCI devices to your guests.

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