[libvirt] [PATCH 1/9] conf: add <irqchip mode> to <features>

[Ján Tomko]

On Tue, Mar 28, 2017 at 02:50:58PM -0400, John Ferlan wrote:
>On 03/23/2017 11:26 AM, Ján Tomko wrote:
>> @@ -1788,6 +1789,15 @@
>>            for hypervisor to decide.
>>            <span class="since">Since 2.1.0</span>
>>        </dd>
>> +      <dt><code>irqchip</code></dt>
>> +      <dd>Tune the in-kernel irqchip. Possible values for the
>> +          <code>mode</code> attribute are:
>> +          <code>on</code>, <code>split</code> and <code>off</code>.
>> +          <code>split</code> is useful for using interrupt remapping
>> +          with the <a href="#elementsIommu">IOMMU device</a>.
>> +          The default is left for hypervisor to decide.
>> +          <span class="since">Since 3.3.0</span> (QEMU only)
>> +      </dd>
>
>Did you somehow know this wouldn't be reviewed in time for 3.2.0?  ;-)
>
>Once I got to patch 4 & 7, I began to wonder if support there was
>dependence upon the value being "split" or is "on" also acceptable. It
>would seem "off" and not present wouldn't allow intremap or caching to
>work.
>

Looking at QEMU code, off also works but it seems the restriction is
temporary.

>At the very least whatever it is that allows the -device intel-iommu to
>be present in QEMU 2.7 (if I read virQEMUCapsInitQMPMonitor correctly)
>instead of ",iommu=on" would also seem to be a requirement. I know we
>don't want to put versions there, but whatever it is that is required
>should be listed (at least while it's still fresh in your mind).
>

The intremap option was introduced in QEMU 2.9, so libvirt cannot possibly
support it with 2.7's -machine iommu=on.

Jan
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