[libvirt] [RFC] docs: Discourage usage of cache mode=passthrough

[Laine Stump]

On 09/19/2017 03:37 PM, Eduardo Habkost wrote:
> Cache mode=passthrough can result in a broken cache topology if
> the domain topology is not exactly the same as the host topology.
> Warn about that in the documentation.
>
> Bug report for reference:
> https://bugzilla.redhat.com/show_bug.cgi?id=1184125
>
> Signed-off-by: Eduardo Habkost <ehabkost at redhat.com>
> ---
>  docs/formatdomain.html.in | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 57ec2ff34..9c21892f3 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -1478,7 +1478,9 @@
>  
>                <dt><code>passthrough</code></dt>
>                <dd>The real CPU cache data reported by the host CPU will be
> -                passed through to the virtual CPU.</dd>
> +                passed through to the virtual CPU.  Using this mode is not
> +                recommended unless the domain CPU and NUMA topology is exactly
> +                the same as the host CPU and NUMA topology.</dd>

To me this sounds like it should be forbidden by libvirt, rather than
just documented as "bad". (I haven't followed any previous discussion on
the topic though, so maybe I'm over-reacting).