docs: Deprecate CPU model runnability guarantees

Document that CPU model runnability guarantees won't apply to
unversioned CPU models anymore.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20190628002844.24894-9-ehabkost@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Eduardo Habkost 2019-06-27 21:28:43 -03:00
parent 0788a56bd1
commit aa5b969287

View file

@ -292,3 +292,22 @@ subset of the image.
In the future, QEMU will require Python 3 to be available at
build time. Support for Python 2 in scripts shipped with QEMU
is deprecated.
@section Backwards compatibility
@subsection Runnability guarantee of CPU models (since 4.1.0)
Previous versions of QEMU never changed existing CPU models in
ways that introduced additional host software or hardware
requirements to the VM. This allowed management software to
safely change the machine type of an existing VM without
introducing new requirements ("runnability guarantee"). This
prevented CPU models from being updated to include CPU
vulnerability mitigations, leaving guests vulnerable in the
default configuration.
The CPU model runnability guarantee won't apply anymore to
existing CPU models. Management software that needs runnability
guarantees must resolve the CPU model aliases using te
``alias-of'' field returned by the ``query-cpu-definitions'' QMP
command.