+Jiri, +Daniel, +Igor
On Thu, Apr 29, 2021 at 11:59:41AM +0200, Markus Armbruster wrote:
[...]
> I'm not sure there's anything to remove here, but anyway, Peter Maydell:
>
This one is mine.
There's no code to remove, but the intention is to eventually
change default_cpu_version to CPU_VERSION_LATEST on newer machine
types.
>
> 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.
libvirt had no time to adapt to this yet. As far as I
understand, they need the following series to be merged first so
they can more easily resolve the unversioned CPU model name
aliases:
https://lore.kernel.org/qemu-devel/20201013230457.150630-1-ehabk...@redhat.com
I need to rebase that series and resubmit.
--
Eduardo
