Re: [libvirt] [PATCHv2 3/6] conf: add to

[Ján Tomko]

On Mon, Apr 24, 2017 at 05:42:07PM -0400, John Ferlan wrote:

On 04/20/2017 08:19 AM, Ján Tomko wrote:

Add a new attribute to control interrupt remapping.

https://bugzilla.redhat.com/show_bug.cgi?id=1427005
---
 docs/formatdomain.html.in                          | 22 ++++++++++++-
 docs/schemas/domaincommon.rng                      |  9 +++++
 src/conf/domain_conf.c                             | 38 +++++++++++++++++++---
 src/conf/domain_conf.h                             |  1 +
 .../qemuxml2argv-intel-iommu-irqchip.xml           |  4 ++-
 5 files changed, 68 insertions(+), 6 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index abf089a..f5a8e76 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -7335,7 +7335,9 @@ qemu-kvm -net nic,model=? /dev/null
 <pre>
 ...
 &lt;devices&gt;
-  &lt;iommu model='intel'/&gt;
+  &lt;iommu model='intel'&gt;
+    &lt;driver intremap='on'/&gt;
+  &lt;/iommu&gt;
 &lt;/devices&gt;
 ...
 </pre>
@@ -7346,6 +7348,24 @@ qemu-kvm -net nic,model=? /dev/null
           Currently only the <code>intel</code> model is supported.
         </p>
       </dd>
+      <dt><code>driver</code></dt>
+      <dd>
+        <p>
+          The <code>driver</code> subelement can be used to configure
+          additional options:
+        </p>
+        <dl>
+          <dt><code>intremap</code></dt>
+          <dd>
+            <p>
+              The <code>intremap</code> attribute with possible values
+              <code>on</code> and <code>off</code> can be used to
+              turn on interrupt remapping. <span class="since">Since 
3.3.0</span>
+              (QEMU only)

It seems there is a relationship between this parameter and irqchip
mode? IOW: Is it a requirement that irqchip be "split" or "on"? It's
difficult to ascertain from the bz, but if so, then I'd expect a domain
conf post processing in this patch.

Per http://wiki.qemu.org/Features/VT-d:
Currently, interrupt remapping does not support full kernel irqchip,
only "split" and "off" are supported.

We should not put current QEMU implementation limits into XML post
processing.

Reading the bz it seems though that this parameter is optional for
"certain" devices; however, for "general emulated devices" it's what is
used to enable VT-d protection, but that could also be read as if
'intel-iommu' is enabled, then VT-d protection is on by default with
'intremap' just having some other affect.

Interrupt remapping is part of the VT-d feature.

Is there something we could describe here at a very high level to
describe the usefulness/need for this parameter?

IMO that is out of scope of the element description.

Jan

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