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[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

>From the ubuntu-trusty git repository:

$ git --format=oneline Ubuntu-3.13.0-77.121.. -- drivers/hv

04d1fd1012796e714f3b291fc0487e45d2fbd9ba Drivers: hv: vmbus: Fix a Host signaling bug
952f5d0a5b0f3b032902537a1aeafdee75ac69a6 Drivers: hv: vmbus: Fix a siganlling host signalling issue
c402db4908545dbe6daa1aa7494be37d6b3f4ee3 Drivers: hv: vmbus: Export the vmbus_sendpacket_pagebuffer_ctl()
14df727b252b7f20ffb156edab89d81ebb2b31b5 Drivers: hv: vmbus: Suport an API to send packet with additional control
cb5c01b81dc4b08c9eccd40b2f626a3c7bced6f5 Drivers: hv: vmbus: Suport an API to send pagebuffers with additional control
ee8c7cb858c2e7f2d81d9b87fdfb6ee292b341a9 Drivers: hv: vmbus: Implement per-CPU mapping of relid to channel
a84dc0bfcd6b8d9a217e7c73e89b1e3ed44ac3f8 Drivers: hv: Eliminate the channel spinlock in the callback path

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https://bugs.launchpad.net/bugs/1519897

Title:
  [Hyper-V] hv: vmbus: Fix a host signaling bug

Status in linux package in Ubuntu:
  In Progress
Status in linux-lts-trusty package in Ubuntu:
  In Progress
Status in linux source package in Trusty:
  Fix Committed
Status in linux-lts-trusty source package in Trusty:
  In Progress
Status in linux source package in Wily:
  In Progress
Status in linux source package in Xenial:
  In Progress

Bug description:
  The following fix has been submitted upstream, but has high enough
  severity that we would like early inclusion into the Ubuntu kernel.
  Please consider for wily, vivid, and trusty (and the HWE kernels for
  the same).

  Patch follows:

  Currently we have two policies for deciding when to signal the host:
  One based on the ring buffer state and the other based on what the VMBUS client driver wants to do. Consider the case when the client wants to explicitly control when to signal the host. In this case, if the client were to defer signaling, we will not be able to signal the host subsequently when the client does want to signal since the ring buffer state will prevent the signaling. Implement logic to have only one signaling policy in force for a given channel.

  Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
  Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
  Tested-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
  Cc: <stable@xxxxxxxxxxxxxxx> # v4.2+
  ---
   drivers/hv/channel.c   |   18 ++++++++++++++++++
   include/linux/hyperv.h |   12 ++++++++++++
   2 files changed, 30 insertions(+), 0 deletions(-)

  diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index 77d2579..c6278c7 100644
  --- a/drivers/hv/channel.c
  +++ b/drivers/hv/channel.c
  @@ -653,10 +653,19 @@ int vmbus_sendpacket_ctl(struct vmbus_channel *channel, void *buffer,
     *    on the ring. We will not signal if more data is
     *    to be placed.
     *
  +	 * Based on the channel signal state, we will decide
  +	 * which signaling policy will be applied.
  +	 *
     * If we cannot write to the ring-buffer; signal the host
     * even if we may not have written anything. This is a rare
     * enough condition that it should not matter.
     */
  +
  +	if (channel->signal_state)
  +		signal = true;
  +	else
  +		kick_q = true;
  +
    if (((ret == 0) && kick_q && signal) || (ret))
     vmbus_setevent(channel);

  @@ -756,10 +765,19 @@ int vmbus_sendpacket_pagebuffer_ctl(struct vmbus_channel *channel,
     *    on the ring. We will not signal if more data is
     *    to be placed.
     *
  +	 * Based on the channel signal state, we will decide
  +	 * which signaling policy will be applied.
  +	 *
     * If we cannot write to the ring-buffer; signal the host
     * even if we may not have written anything. This is a rare
     * enough condition that it should not matter.
     */
  +
  +	if (channel->signal_state)
  +		signal = true;
  +	else
  +		kick_q = true;
  +
    if (((ret == 0) && kick_q && signal) || (ret))
     vmbus_setevent(channel);

  diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 437c9c8..7b1af52 100644
  --- a/include/linux/hyperv.h
  +++ b/include/linux/hyperv.h
  @@ -756,8 +756,20 @@ struct vmbus_channel {
     * link up channels based on their CPU affinity.
     */
    struct list_head percpu_list;
  +	/*
  +	 * Host signaling policy: The default policy will be
  +	 * based on the ring buffer state. We will also support
  +	 * a policy where the client driver can have explicit
  +	 * signaling control.
  +	 */
  +	bool signal_state;
   };

  +static inline void set_channel_signal_state(struct vmbus_channel *c,
  +bool state) {
  +	c->signal_state = state;
  +}
  +
   static inline void set_channel_read_state(struct vmbus_channel *c, bool state)  {
    c->batched_reading = state;
  --
  1.7.4.1

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