Re: [Xen-devel] Re: [vt-d][xen4-rc6] Hangs on startup

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 22, 2010 at 03:06:48PM -0600, Nadolski, Ed wrote:
> 
> 
> > -----Original Message-----
>  
> > PCI back is to be used _only_ with PV guests - you on the other
> > hand are running an HVM guest.
> > 
> > Per the earlier statement, I would recommend you use the 'pciback'
> > instead of 'pci-stub' or just not compile pciback in and see what
> > happens. Keep in mind: PCI back module is only needed when you want to
> > do PV PCI passthrough, which is not what you are doing.
> 
> I'm confused - does that mean pci-stub must be used for device assignment to 
> an HVM guest?  The VTdHowTo isn't clear on that.

Not per say.

xen-pciback can be used for both PV and HVM.
pci-stub can only be used for HVM guests.

But there seems to be a bug somewhere that when the PCI device is
assigned to pci-stub, pciback tries to seize it and can't find it and
somehow is stuck in a spin-lock.  That shouldn't be happening.

Right now I am trying to figure out if we remove from Lukasza system
pciback and only use pci-stub whether he still gets those MFN lookup
errors with his QLogic card. Those are, I believe, a seperate issue from
the pciback spinlock failure.

> 
> Is there a way to bind the PCI devices to pci-stub at boot time, like with 
> pciback? 

No.
> Also, do the 'xm pci-list-assignable-devices' and 'xm pci-list' commands work 
> the same for both pciback and pci-stub bindings?

Yes.
> 
> It seems odd to have different ways to do bindings for PV and for HVM. For 
> example, would I have to switch the bindings if I want to first assign a 
> device to a PV guest, then stop the PV guest and re-assign the device to an 
> HVM guest?

No if you use 'xen-pciback'. Yes if you use 'pci-stub'.

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