Re: Let's remove some deprecated stuff

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 29 Apr 2021 at 11:02, Markus Armbruster <armbru@redhat.com> wrote:
>
> If you're cc'ed, you added a section to docs/system/deprecated.rst that
> is old enough to permit removal.  This is *not* a demand to remove, it's
> a polite request to consider whether the time for removal has come.
> Extra points for telling us in a reply.  "We should remove, but I can't
> do it myself right now" is a valid answer.  Let's review the file:

> I'm not sure there's anything to remove here, but anyway, Peter Maydell:

This isn't one of mine -- I just show up in git blame because this
section predates the conversion from texi to rst. It was originally
added by Eduardo (cc'd) in commit aa5b9692871.

>     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 the
>     ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
>     command.
>
>     While those guarantees are kept, the return value of
>     ``query-cpu-definitions`` will have existing CPU model aliases
>     point to a version that doesn't break runnability guarantees
>     (specifically, version 1 of those CPU models).  In future QEMU
>     versions, aliases will point to newer CPU model versions
>     depending on the machine type, so management software must
>     resolve CPU model aliases before starting a virtual machine.

thanks
-- PMM