Re: [PATCH qemu] qxl: COLO secondary node not need to release resources

[Gerd Hoffmann]

> During COLO checkpoint, the Secondary VM's qemu has loaded Primary
> VM's qxl states, so it not need to release qxl resources.

> +#include "migration/colo.h"
>  #include "trace.h"
>  
>  #include "qxl.h"
> @@ -757,6 +758,10 @@ static void interface_release_resource(QXLInstance *sin,
>      if (!ext.info) {
>          return;
>      }
> +    /* The SVM load PVM states,so it not need to release resources */
> +    if (get_colo_mode() == COLO_MODE_SECONDARY) {
> +        return;
> +    }
>      if (ext.group_id == MEMSLOT_GROUP_HOST) {
>          /* host group -> vga mode update request */
>          QXLCommandExt *cmdext = (void *)(intptr_t)(ext.info->id);
> @@ -880,6 +885,10 @@ static int interface_flush_resources(QXLInstance *sin)
>      PCIQXLDevice *qxl = container_of(sin, PCIQXLDevice, ssd.qxl);
>      int ret;
>  
> +    /* The SVM load PVM states,so it not need to release resources */
> +    if (get_colo_mode() == COLO_MODE_SECONDARY) {
> +        return 0;
> +    }
>      ret = qxl->num_free_res;
>      if (ret) {
>          qxl_push_free_res(qxl, 1);

Hmm, not sure what to do with this one.  I know next to nothing about
COLO, but I suspect this is just papering over the root cause.

Some qxl functionality is handed by a thread started by libspice-server.
The thread can be started and stopped (see qemu_spice_display_start,
qemu_spice_display_stop).  There is a handler (vm_change_state_handler)
which starts/stops depending on vm state, specifically the thread is
stopped when saving+loading vmstate to avoid problems simliar to the one
you are seeing with colo.

What I think you need is proper management of that thread when colo is
active.  Possibly it should just never be active on a secondary node,
but I don't know enough about colo to be sure.

HTH & take care,
  Gerd