Re: [PATCH v1 1/3] virtio-balloon: fix free page hinting without an iothread

[David Hildenbrand <david@redhat.com>]

On 18.05.20 17:01, Alexander Duyck wrote:
> On Mon, May 18, 2020 at 1:37 AM David Hildenbrand <david@redhat.com> wrote:
>>
>> In case we don't have an iothread, we mark the feature as abscent but
>> still add the queue. 'free_page_bh' remains set to NULL.
>>
>> qemu-system-i386 \
>>         -M microvm \
>>         -nographic \
>>         -device virtio-balloon-device,free-page-hint=true \
>>         -nographic \
>>         -display none \
>>         -monitor none \
>>         -serial none \
>>         -qtest stdio
>>
>> Doing a "write 0xc0000e30 0x24
>> 0x030000000300000003000000030000000300000003000000030000000300000003000000"
>>
>> We will trigger a SEGFAULT. Let's move the check and bail out.
>>
>> While at it, move the static initializations to instance_initialize().
>>
>> Fixes: c13c4153f76d ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
>> Reported-by: Alexander Bulekov <alxndr@bu.edu>
>> Cc: Wei Wang <wei.w.wang@intel.com>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
>> Cc: Alexander Duyck <alexander.duyck@gmail.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  hw/virtio/virtio-balloon.c | 35 ++++++++++++++++++-----------------
>>  1 file changed, 18 insertions(+), 17 deletions(-)
>>
>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
>> index 065cd450f1..dc3b1067ab 100644
>> --- a/hw/virtio/virtio-balloon.c
>> +++ b/hw/virtio/virtio-balloon.c
>> @@ -789,6 +789,13 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>>          return;
>>      }
>>
>> +    if (virtio_has_feature(s->host_features,
>> +        VIRTIO_BALLOON_F_FREE_PAGE_HINT) && !s->iothread) {
>> +        error_setg(errp, "'free-page-hint' requires 'iothread' to be set");
>> +        virtio_cleanup(vdev);
>> +        return;
>> +    }
>> +
>>      s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>>      s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>>      s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
>> @@ -797,24 +804,11 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>>                             VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
>>          s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
>>                                             virtio_balloon_handle_free_page_vq);
>> -        s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
>> -        s->free_page_report_cmd_id =
>> -                           VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
>> -        s->free_page_report_notify.notify =
>> -                                       virtio_balloon_free_page_report_notify;
>>          precopy_add_notifier(&s->free_page_report_notify);
>> -        if (s->iothread) {
>> -            object_ref(OBJECT(s->iothread));
>> -            s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),
>> -                                       virtio_ballloon_get_free_page_hints, s);
>> -            qemu_mutex_init(&s->free_page_lock);
>> -            qemu_cond_init(&s->free_page_cond);
>> -            s->block_iothread = false;
>> -        } else {
>> -            /* Simply disable this feature if the iothread wasn't created. */
>> -            s->host_features &= ~(1 << VIRTIO_BALLOON_F_FREE_PAGE_HINT);
>> -            virtio_error(vdev, "iothread is missing");
>> -        }
>> +
>> +        object_ref(OBJECT(s->iothread));
>> +        s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),
>> +                                     virtio_ballloon_get_free_page_hints, s);
>>      }
>>      reset_stats(s);
>>  }
>> @@ -892,6 +886,13 @@ static void virtio_balloon_instance_init(Object *obj)
>>  {
>>      VirtIOBalloon *s = VIRTIO_BALLOON(obj);
>>
>> +    qemu_mutex_init(&s->free_page_lock);
>> +    qemu_cond_init(&s->free_page_cond);
>> +    s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
>> +    s->free_page_report_cmd_id = VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
>> +    s->free_page_report_notify.notify = virtio_balloon_free_page_report_notify;
>> +    s->block_iothread = false;
>> +
>>      object_property_add(obj, "guest-stats", "guest statistics",
>>                          balloon_stats_get_all, NULL, NULL, s);
>>
> 
> So the one nit I have is that I am not sure you need to bother with
> initializing block_iothread since it should already be initialized to
> false/0 shouldn't it? Otherwise this all looks good to me.

Yes, and as "FREE_PAGE_REPORT_S_STOP = 0", that's implicitly set as
well. Both can go IMHO.

> 
> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 

Thanks!

-- 
Thanks,

David / dhildenb