[PATCH v2 1/1] qemuProcessRefreshCPU: skip 'host-model' logic for pSeries guests

[Jiri Denemark]

On Mon, May 25, 2020 at 09:39:45 -0300, Daniel Henrique Barboza wrote:
> Commit v3.10.0-182-g237f045d9a ("qemu: Ignore fallback CPU attribute
> on reconnect") forced CPU 'fallback' to ALLOW, regardless of user
> choice. This fixed a situation in which guests created with older
> Libvirt versions, which used CPU mode 'host-model' in runtime, would
> fail to launch in a newer Libvirt if the fallback was set to FORBID.
> This would lead to a scenario where the CPU was translated to 'host-model'
> to 'custom', but then the FORBID setting would make the translation
> process fail.
> 
> PSeries can operate with 'host-model' in runtime due to specific PPC64
> mechanics regarding compatibility mode. The update() implementation of
> the cpuDriverPPC64 driver is a NO-OP if CPU mode is 'host-model', and
> the driver does not implement translate(). The commit mentioned above
> is causing PSeries guests to get their 'fallback' setting to ALLOW,
> overwriting user choice, exposing a design problem in
> qemuProcessRefreshCPU() - for PSeries guests, handling 'host-model'
> as it is being done does not apply.
> 
> All other cpuArchDrivers implements update() and changes guest mode
> to VIR_CPU_MODE_CUSTOM, meaning that PSeries is currently the only
> exception to this logic. Let's make it official.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1660711
> 
> Suggested-by: Jiri Denemark <jdenemar at redhat.com>
> Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> ---
>  src/qemu/qemu_process.c | 9 +++++++++
>  1 file changed, 9 insertions(+)

Reviewed-by: Jiri Denemark <jdenemar at redhat.com>

Thanks and pushed.