[Qemu-devel] [PATCH] balloon: Do not save VM state wrt asynchronous virtio operations

[Qemu-devel] [PATCH] balloon: Do not save VM state wrt asynchronous virtio operations

[Adam Litke]

When working with the VM state (for loadvm/savevm and migration), it is not
valid to load and store pointers since the validity of those pointers cannot be
assured in the new qemu address space.  Therefore, virtio_balloon_save() and
virtio_balloon_load() must not handle the stats-related fields in struct
VirtIOBalloon.

If a memory stats request is in-flight at the time of a migration or savevm,
the request will not complete and should be resubmitted once migration or
loadvm completes.  Note that this extremely small race window can only be
triggered using QMP so it is not possible to hang the user monitor.
    
Signed-off-by: Adam Litke <agl@us.ibm.com>

diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index 086d9d1..6d12024 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -261,10 +261,6 @@ static void virtio_balloon_save(QEMUFile *f, void *opaque)
 
     qemu_put_be32(f, s->num_pages);
     qemu_put_be32(f, s->actual);
-    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
-    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
-    qemu_put_buffer(f, (uint8_t *)&s->stats_callback, sizeof(MonitorCompletion));
-    qemu_put_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, sizeof(void));
 }
 
 static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
@@ -278,11 +274,6 @@ static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
 
     s->num_pages = qemu_get_be32(f);
     s->actual = qemu_get_be32(f);
-    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
-    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
-    qemu_get_buffer(f, (uint8_t *)&s->stats_callback, sizeof(MonitorCompletion));
-    qemu_get_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, sizeof(void));
-
     return 0;
 }
 


-- 
Thanks,
Adam

[Qemu-devel] Re: [PATCH] balloon: Do not save VM state wrt asynchronous virtio operations

[Juan Quintela]

Adam Litke <agl@us.ibm.com> wrote:
> When working with the VM state (for loadvm/savevm and migration), it is not
> valid to load and store pointers since the validity of those pointers cannot be
> assured in the new qemu address space.  Therefore, virtio_balloon_save() and
> virtio_balloon_load() must not handle the stats-related fields in struct
> VirtIOBalloon.
>
> If a memory stats request is in-flight at the time of a migration or savevm,
> the request will not complete and should be resubmitted once migration or
> loadvm completes.  Note that this extremely small race window can only be
> triggered using QMP so it is not possible to hang the user monitor.
>     
> Signed-off-by: Adam Litke <agl@us.ibm.com>

Acked-by: Juan Quintela <quintela@redhat.com>

Re: [Qemu-devel] [PATCH] balloon: Do not save VM state wrt asynchronous virtio operations

[Anthony Liguori]

On 03/09/2010 12:54 PM, Adam Litke wrote:
> When working with the VM state (for loadvm/savevm and migration), it is not
> valid to load and store pointers since the validity of those pointers cannot be
> assured in the new qemu address space.  Therefore, virtio_balloon_save() and
> virtio_balloon_load() must not handle the stats-related fields in struct
> VirtIOBalloon.
>
> If a memory stats request is in-flight at the time of a migration or savevm,
> the request will not complete and should be resubmitted once migration or
> loadvm completes.  Note that this extremely small race window can only be
> triggered using QMP so it is not possible to hang the user monitor.
>
> Signed-off-by: Adam Litke<agl@us.ibm.com>
>    
Applied.  Thanks.

Regards,

Anthony Liguori
> diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
> index 086d9d1..6d12024 100644
> --- a/hw/virtio-balloon.c
> +++ b/hw/virtio-balloon.c
> @@ -261,10 +261,6 @@ static void virtio_balloon_save(QEMUFile *f, void *opaque)
>
>       qemu_put_be32(f, s->num_pages);
>       qemu_put_be32(f, s->actual);
> -    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
> -    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
> -    qemu_put_buffer(f, (uint8_t *)&s->stats_callback, sizeof(MonitorCompletion));
> -    qemu_put_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, sizeof(void));
>   }
>
>   static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
> @@ -278,11 +274,6 @@ static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
>
>       s->num_pages = qemu_get_be32(f);
>       s->actual = qemu_get_be32(f);
> -    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
> -    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
> -    qemu_get_buffer(f, (uint8_t *)&s->stats_callback, sizeof(MonitorCompletion));
> -    qemu_get_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, sizeof(void));
> -
>       return 0;
>   }
>
>
>
>