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From: Alex Williamson <alex.williamson@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 3/3] IOMMU: Integrate between VFIO and
 vIOMMU to support device assignment
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To: "Aviv B.D." <bd.aviv@gmail.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Peter Xu <peterx@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

On Thu, 02 Jun 2016 13:09:27 +0000
"Aviv B.D." <bd.aviv@gmail.com> wrote:

> Hi,
> 
> In case of hot plug vfio device there should not be any active mapping
> to this device prior the device addition.

Counter example - a device is hot added to a guest booted with iommu=pt.

> Also before it added to a guest
> the guest should not attach the device to any domain as the device is not
> present.

The static identity map domain (ie. passthrough domain) can precede the
device existing.

> With CM enabled the guest must invalidate the domain or individual mappings
> that belong to this new device before any use of those maps.
> 
> I'm still not sure that this functionality is necessary in x86 and
> currently there
> is a scenario (for x86) that use this functionality.

Clearly I disagree, it is necessary.  Thanks,

Alex