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Date: Tue, 18 Apr 2017 12:54:00 +0800
From: Peter Xu <peterx@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 7/7] intel_iommu: support passthrough
 (PT)
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To: "Liu, Yi L" <yi.l.liu@intel.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "Lan, Tianyu" <tianyu.lan@intel.com>, "Michael S . Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, Marcel Apfelbaum <marcel@redhat.com>, David Gibson <david@gibson.dropbear.id.au>

On Tue, Apr 18, 2017 at 04:30:40AM +0000, Liu, Yi L wrote:

[...]

> > +static void vtd_switch_address_space(VTDAddressSpace *as) {
> > +    bool use_iommu;
> > +
> > +    assert(as);
> > +
> > +    use_iommu = as->iommu_state->dmar_enabled;
> > +    if (use_iommu) {
> > +        /* Further checks per-device configuration */
> > +        use_iommu &= !vtd_dev_pt_enabled(as);
> > +    }
> > +
> > +    trace_vtd_switch_address_space(pci_bus_num(as->bus),
> > +                                   VTD_PCI_SLOT(as->devfn),
> > +                                   VTD_PCI_FUNC(as->devfn),
> > +                                   use_iommu);
> 
> Hi Peter,
> 
> Skip address space switching is a good idea to support Passthru mode.
> However, without the address space, the vfio notifier would not be
> registered, thus vIOMMU emulator has no way to connect to host. It is
> no harm if there is only map/unmap notifier. But if we have more notifiers
> other than map/unmap, it may be a problem.
> 
> I think we need to reconsider it here. 

For now I think as switching is good to us in general. Could I know
more context about this? Would it be okay to work on top of this in
the future?

Thanks,

-- 
Peter Xu