Re: [Xen-devel] [PATCH] QEMU as non-root and PCI passthrough do not mix

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 15 Jan 2016, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 15, 2016 at 02:14:40PM +0000, Stefano Stabellini wrote:
> > On Thu, 14 Jan 2016, Ian Jackson wrote:
> > > Stefano Stabellini writes ("Re: [PATCH] QEMU as non-root and PCI 
> > > passthrough do not mix"):
> > > > On Thu, 14 Jan 2016, Ian Campbell wrote:
> > > > > What if b_info->device_model_user is NULL or == "root"? Doesn't this 
> > > > > warn
> > > > > even then?
> > > > 
> > > > I meant to warn even if device_model_user is NULL because it is the
> > > > default and I think it is fair to inform the user about this. But I
> > > > think you are right that we don't want to warn if device_model_user is
> > > > specified as "root".
> > > 
> > > Much of the logic here is upended by what is now my qemu privsep
> > > series.  Is it really worth fine-tuning the default handling here ?
> > 
> > Fair enough.
> > 
> > Do you prefer the PCI passthrough case to be fixed now or after your
> > series? In other words, do you prefer this patch to go in now, or after
> > your series?
> 
> I hadn't chance to look at the patch but I was wondering if we also
> take into account the pci-assign and pci-detach on a guest that booted
> without PCI passthrough?

A guest booted without PCI passthrough, with QEMU running as root, would
work as usual. But if QEMU is running as non-root, pci-assign wouldn't
work. The errors printed out by xl and QEMU respectively are the
followings:

libxl: error: libxl_qmp.c:287:qmp_handle_error_response: received an
error message from QMP server: Device initialization failed

[00:03.0] xen_pt_initfn: Error: Failed to "open" the real pci device. rc: -13

In this patch I only added one more debugging message to pci-assign,
informing the user that pci-assign requires QEMU running as root.

After IanJ series we'll be able to do better.

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