diff mbox series

[v2,8/9] docs: Deprecate CPU model runnability guarantees

Message ID 20190628002844.24894-9-ehabkost@redhat.com
State New
Headers show
Series x86 CPU model versioning | expand

Commit Message

Eduardo Habkost June 28, 2019, 12:28 a.m. UTC 
Document that CPU model runnability guarantees won't apply to
unversioned CPU models anymore.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
Changes v1 -> v2:
* (none)

Cc: libvir-list@redhat.com
---
 qemu-deprecated.texi | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Comments

Daniel P. Berrangé July 2, 2019, 9:46 a.m. UTC | #1 
On Thu, Jun 27, 2019 at 09:28:43PM -0300, Eduardo Habkost wrote:
> Document that CPU model runnability guarantees won't apply to
> unversioned CPU models anymore.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
> Changes v1 -> v2:
> * (none)
> 
> Cc: libvir-list@redhat.com
> ---
>  qemu-deprecated.texi | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)


Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
diff mbox series

Patch

diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
index 9cba82d5ec..18f85f70e1 100644
--- a/qemu-deprecated.texi
+++ b/qemu-deprecated.texi
@@ -276,3 +276,22 @@  Note that if you are exposing the export via /dev/nbd0, it is easier
 to just export the entire image and then mount only /dev/nbd0p1 than
 it is to reinvoke @command{qemu-nbd -c /dev/nbd0} limited to just a
 subset of the image.
+
+@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.