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[Qemu-devel] [PULL v4 39/43] docs: Deprecate CPU model runnability guara

From: Eduardo Habkost
Subject: [Qemu-devel] [PULL v4 39/43] docs: Deprecate CPU model runnability guarantees
Date: Wed, 3 Jul 2019 15:07:22 -0300

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

Signed-off-by: Eduardo Habkost <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Daniel P. Berrangé <address@hidden>
Signed-off-by: Eduardo Habkost <address@hidden>
 qemu-deprecated.texi | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

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

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