Re: [libvirt] [PATCHv2 3/6] conf: add <driver intremap> to <iommu>

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.

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.

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