Hi Sean,
On 11/27/2017 03:25 PM, Mooney, Sean K wrote:
Sean can confirm, but my reading is that Sean's primary concern is with
the proposal to add any config option to enable iommu - not with the
proposal to change from a per port to per OVS basis.
[Mooney, Sean K] so I had a quick chat with mark about the background to this.
My current understanding is that form qemu 2.6-2.9 there is a bug that causes
the
Guest to hang due to a lack of support for a required ack to correctly
negotiate the
Use of the iommu feature. As a result a config option either global or per
interfaces is
Required. As an aside OpenStack does not currently support requesting iommu
virtualization so
I don’t see why we could not put a requirement on our side that you use qemu
2.9.1 or newer
To avail of that feature. Going back to ovs then assuming we used a single
global config vaule
In for example the other_config dictionary of the Open_vSwitch table in the
ovsdb.
e.g. ovs-vsctl set Open_vswitch . other_config:vhost-iommu-support=true
I would be fine with that approach if we can confirm 1 thing first.
I confirm you understanding:
1. Before Qemu v2.9.1, we must not enable iommu-support option because
because it enables a vhost-user protocol feature (reply-ack) that is
suffers from a bug in these Qemu version. And this is not a problem
because iommu isn't anyway supported in these Qemu versions.
2. Since Qemu v2.9.1, the reply-ack bug has been fixed, so we can enable
iommu-support option safely, using iommu or not.
Regards,
Maxime
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