• Ladi Prosek's avatar
    virtio_balloon: init 1st buffer in stats vq · 6918f844
    Ladi Prosek authored
    commit fc865322 upstream.
    
    When init_vqs runs, virtio_balloon.stats is either uninitialized or
    contains stale values. The host updates its state with garbage data
    because it has no way of knowing that this is just a marker buffer
    used for signaling.
    
    This patch updates the stats before pushing the initial buffer.
    
    Alternative fixes:
    * Push an empty buffer in init_vqs. Not easily done with the current
      virtio implementation and violates the spec "Driver MUST supply the
      same subset of statistics in all buffers submitted to the statsq".
    * Push a buffer with invalid tags in init_vqs. Violates the same
      spec clause, plus "invalid tag" is not really defined.
    
    Note: the spec says:
    	When using the legacy interface, the device SHOULD ignore all values in
    	the first buffer in the statsq supplied by the driver after device
    	initialization. Note: Historically, drivers supplied an uninitialized
    	buffer in the first buffer.
    
    Unfortunately QEMU does not seem to implement the recommendation
    even for the legacy interface.
    Signed-off-by: default avatarLadi Prosek <lprosek@redhat.com>
    Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
    6918f844
virtio_balloon.c 9.96 KB