Re: [PATCH] vfio/migrate: Move switch of dirty tracking into vfio_memory_listener

[Paolo Bonzini]

On 11/01/21 08:34, Keqian Zhu wrote:
> +static void vfio_listener_log_start(MemoryListener *listener,
> +                                    MemoryRegionSection *section,
> +                                    int old, int new)
> +{
> +    VFIOContainer *container = container_of(listener, VFIOContainer, listener);
> +
> +    vfio_set_dirty_page_tracking(container, true);
> +}
> +
> +static void vfio_listener_log_stop(MemoryListener *listener,
> +                                   MemoryRegionSection *section,
> +                                   int old, int new)
> +{
> +    VFIOContainer *container = container_of(listener, VFIOContainer, listener);
> +
> +    vfio_set_dirty_page_tracking(container, false);
> +}
> +

This would enable dirty page tracking also just for having a framebuffer 
(DIRTY_MEMORY_VGA).  Technically it would be correct, but it would also 
be more heavyweight than expected.

In order to only cover live migration, you can use the log_global_start 
and log_global_stop callbacks instead.

If you want to use log_start and log_stop, you need to add respectively

    if (old != 0) {
        return;
    }

and

    if (new != 0) {
        return;
    }

before the calls to vfio_set_dirty_page_tracking.  But I think it's more 
appropriate for VFIO to use log_global_*.

Thanks,

Paolo