[libvirt] [PATCH 5/6] qemu: migration: warn if migrating with host-passthrough

[Jiri Denemark]

On Mon, Nov 21, 2016 at 14:11:55 -0500, Jason J. Herne wrote:
> From: "Collin L. Walling" <walling at linux.vnet.ibm.com>
> 
> Warn the user when migrating a guest that is using the host-passthrough cpu
> mode. host-passthrough is not migration safe because the host hypervisor is not
> attempting to block features that may not exist on the destination host.
> 
> Signed-off-by: Collin L. Walling <walling at linux.vnet.ibm.com>
> Signed-off-by: Jason J. Herne <jjherne at linux.vnet.ibm.com>
> ---
>  src/qemu/qemu_migration.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index d4a55d8..f721de7 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -3151,6 +3151,10 @@ qemuMigrationBeginPhase(virQEMUDriverPtr driver,
>      if (priv->job.asyncJob == QEMU_ASYNC_JOB_MIGRATION_OUT)
>          qemuMigrationJobSetPhase(driver, vm, QEMU_MIGRATION_PHASE_BEGIN3);
>  
> +    if (vm->def->cpu && vm->def->cpu->mode == VIR_CPU_MODE_HOST_PASSTHROUGH)
> +        VIR_WARN("cpu mode 'host-passthrough' may fail migration if destination"
> +                 " machine is running an older cpu model.");
> +

The warning is not user visible anyway, so there's no real benefit in
adding it. We could document it in formatdomain.html#elementsCPU,
though.

>      if (!qemuMigrationIsAllowed(driver, vm, true, flags))
>          goto cleanup;
>  

Jirka