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Re: [Xen-devel] Re: APIC rework

On Wed, Nov 25, 2009 at 10:43:47AM +0800, Zhang, Xiantao wrote:
> Konrad Rzeszutek Wilk wrote:
> >> At least dom0 parses this info from DSDT, so we can't have the
> >> assuption whether it is used or not, I think. And I also agree to
> >> add a new physdev_op to handle this case, and it should be better
> >> way to go.   
> >> Based on this idea, I worked out the patch, attached!  In this
> >> patch, we introduced a new physdev_op PHYSDEVOP_setup_gsi for each
> >> GSI setup, and each domain can require to map each GSI in this case.
> >> In addition, I believe it is very safe to port the hypervisor patch
> >> to xen-3.4-x tree and keeps pv_ops dom0 running on it, since no
> >> logic is changed.  BTW, I also tested apic and non-apic cases, they
> >> works fine after applying the patches.   
> > 
> > But I don't think you tested PCI front and PCI back.
> > 
> > Mainly these lines worry me (can you inline the patch next time too,
> > please): 
> > 
> > +               map_irq.domid = DOMID_SELF;
> > +               map_irq.type = MAP_PIRQ_TYPE_GSI;
> > +               map_irq.index = gsi;
> > +               map_irq.pirq = irq;
> > +               rc = HYPERVISOR_physdev_op(PHYSDEVOP_map_pirq,
> > &map_irq); 
> > 
> > For PCI passthrough to work, the domid needs to be for the guest
> > domain, while in this case it is set to Dom0.
> > There is already a method of extracting the domain id for PCI devices
> > passed to the guest. Look in the 'xen_create_msi_irq' function.
> Could you detail the concern ?  This hypercall is only related to GSI, not 
> MSI, why it has side-effect about pci passthrough ? 

This is for PV guests _without_ using QEMU. They are using the PCI backend to 
a device (drivers/xen/pciback and drivers/pci/xen-pcifront.c).
The front and back-end communicate the IRQ number (GSI) to the guest
when enabling a INTx PCI device (not MSI ones).

Then the PV guest can bind the IRQ (GSI) number to its own event channel and
have fully working PCI device.

With your change, the privileged domain pins the device to itself, not to
other domains.

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