On Tue, Jun 12, 2018 at 10:58:46AM +0200, Kashyap Chamarthy wrote: > Eduardo Habkost has pointed out that the current documentation of > libvirt's CPU feature policy "require" vs. "force" does not match > QEMU's behaviour. > > Update the documentation by spelling out the QEMU version dependency and > explain in which scenarios the usage of "policy = 'force'" is applicable > or not. > > Signed-off-by: Kashyap Chamarthy <kchamart@xxxxxxxxxx> > --- > Wordsmithing / corrections welcome. > --- > docs/formatdomain.html.in | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in > index 6912762f28..4d6c3892ee 100644 > --- a/docs/formatdomain.html.in > +++ b/docs/formatdomain.html.in > @@ -1566,8 +1566,17 @@ > > <dl> > <dt><code>force</code></dt> > - <dd>The virtual CPU will claim the feature is supported regardless > - of it being supported by host CPU.</dd> > + <dd>The virtual CPU will claim the feature is supported > + regardless of it being supported by host CPU -- this is only > + true for QEMU version older than 2.9.0. I.e. when using the This isn't true for any QEMU versions. QEMU never enables a feature if it's not supported by the host. > + CPU mode 'host-model', libvirt identifies which CPU features > + to use by looking at host CPUID. For that to take effect, it > + is mandatory to use <code>force</code> to tell libvirt that a > + said CPU feature must be used despite it not existing in the > + host -- this applicable only for a very limited set of CPU > + features, such as 'x2apic', virt-ssbd' (for AMD CPUs).</dd> > + <dd>However, when using QEMU 2.9.0 and above, there should > + never be any need to use <code>force</code>.</dd> > <dt><code>require</code></dt> > <dd>Guest creation will fail unless the feature is supported by the > host CPU or the hypervisor is able to emulate it.</dd> > -- > 2.17.0 > -- Eduardo -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
