Re: [PATCH v2] hv: account for packet descriptor in maximum packet size

[Andrea Parri]

(Extending Cc: list,)

On Sun, Jan 09, 2022 at 05:55:16PM +0800, Yanming Liu wrote:
> Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V
> out of the ring buffer") introduced a notion of maximum packet size in
> vmbus channel and used that size to initialize a buffer holding all
> incoming packet along with their vmbus packet header. Currently, some
> vmbus drivers set max_pkt_size to the size of their receive buffer
> passed to vmbus_recvpacket, however vmbus_open expects this size to also
> include vmbus packet header. This leads to corruption of the ring buffer
> state when receiving a maximum sized packet.
> 
> Specifically, in hv_balloon I have observed of a dm_unballoon_request
> message of 4096 bytes being truncated to 4080 bytes. When the driver
> tries to read next packet it starts from a wrong read_index, receives
> garbage and prints a lot of "Unhandled message: type: <garbage>" in
> dmesg.
> 
> The same mismatch also happens in hv_fcopy, hv_kvp, hv_snapshot,
> hv_util, hyperv_drm and hyperv_fb, though bad cases are not observed
> yet.
> 
> Allocate the buffer with HV_HYP_PAGE_SIZE more bytes to make room for
> the descriptor, assuming the vmbus packet header will never be larger
> than HV_HYP_PAGE_SIZE. This is essentially free compared to just adding
> 'sizeof(struct vmpacket_descriptor)' because these buffers are all more
> than HV_HYP_PAGE_SIZE bytes so kmalloc rounds them up anyway.
> 
> Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer")
> Suggested-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> Signed-off-by: Yanming Liu <yanminglr@xxxxxxxxx>

Thanks for sorting this out; the patch looks good to me:

Reviewed-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>

In future submissions (if any), please include LKML as well as subsystem
lists&maintainers; scripts/get_maintainer.pl can be useful to this end.

  Andrea


> ---
> v2: Changed to modify max_pkt_size in individual drivers instead of in
> vmbus code as suggested by Andrea Parri.
> 
>  drivers/gpu/drm/hyperv/hyperv_drm_proto.c |  2 ++
>  drivers/hv/hv_balloon.c                   |  7 +++++++
>  drivers/hv/hv_fcopy.c                     |  2 +-
>  drivers/hv/hv_kvp.c                       |  2 +-
>  drivers/hv/hv_snapshot.c                  |  2 +-
>  drivers/hv/hv_util.c                      | 17 +++++++++++++++++
>  drivers/video/fbdev/hyperv_fb.c           |  2 ++
>  7 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> index c0155c6271bf..bf1548054276 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> @@ -478,6 +478,8 @@ int hyperv_connect_vsp(struct hv_device *hdev)
>  	struct drm_device *dev = &hv->dev;
>  	int ret;
>  
> +	hdev->channel->max_pkt_size = HV_HYP_PAGE_SIZE + VMBUS_MAX_PACKET_SIZE;
> +
>  	ret = vmbus_open(hdev->channel, VMBUS_RING_BUFSIZE, VMBUS_RING_BUFSIZE,
>  			 NULL, 0, hyperv_receive, hdev);
>  	if (ret) {
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index ca873a3b98db..ee2527c3d3b8 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1660,6 +1660,13 @@ static int balloon_connect_vsp(struct hv_device *dev)
>  	unsigned long t;
>  	int ret;
>  
> +	/*
> +	 * max_pkt_size should be large enough for one vmbus packet header plus
> +	 * our receive buffer size. We assume vmbus packet header is smaller
> +	 * than HV_HYP_PAGE_SIZE.
> +	 */
> +	dev->channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +
>  	ret = vmbus_open(dev->channel, dm_ring_size, dm_ring_size, NULL, 0,
>  			 balloon_onchannelcallback, dev);
>  	if (ret)
> diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
> index 660036da7449..07a508ce65db 100644
> --- a/drivers/hv/hv_fcopy.c
> +++ b/drivers/hv/hv_fcopy.c
> @@ -349,7 +349,7 @@ int hv_fcopy_init(struct hv_util_service *srv)
>  {
>  	recv_buffer = srv->recv_buffer;
>  	fcopy_transaction.recv_channel = srv->channel;
> -	fcopy_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +	fcopy_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 3;
>  
>  	/*
>  	 * When this driver loads, the user level daemon that
> diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
> index c698592b83e4..b85d725ae5b1 100644
> --- a/drivers/hv/hv_kvp.c
> +++ b/drivers/hv/hv_kvp.c
> @@ -757,7 +757,7 @@ hv_kvp_init(struct hv_util_service *srv)
>  {
>  	recv_buffer = srv->recv_buffer;
>  	kvp_transaction.recv_channel = srv->channel;
> -	kvp_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 4;
> +	kvp_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 5;
>  
>  	/*
>  	 * When this driver loads, the user level daemon that
> diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
> index 6018b9d1b1fb..dba6baacbf17 100644
> --- a/drivers/hv/hv_snapshot.c
> +++ b/drivers/hv/hv_snapshot.c
> @@ -375,7 +375,7 @@ hv_vss_init(struct hv_util_service *srv)
>  	}
>  	recv_buffer = srv->recv_buffer;
>  	vss_transaction.recv_channel = srv->channel;
> -	vss_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +	vss_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 3;
>  
>  	/*
>  	 * When this driver loads, the user level daemon that
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index 835e6039c186..a7b88c067c07 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -112,6 +112,8 @@ static int hv_shutdown_init(struct hv_util_service *srv)
>  
>  	hibernation_supported = hv_is_hibernation_supported();
>  
> +	channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +
>  	return 0;
>  }
>  
> @@ -133,9 +135,11 @@ static struct hv_util_service util_timesynch = {
>  	.util_deinit = hv_timesync_deinit,
>  };
>  
> +static int heartbeat_init(struct hv_util_service *src);
>  static void heartbeat_onchannelcallback(void *context);
>  static struct hv_util_service util_heartbeat = {
>  	.util_cb = heartbeat_onchannelcallback,
> +	.util_init = heartbeat_init,
>  };
>  
>  static struct hv_util_service util_kvp = {
> @@ -553,6 +557,15 @@ static void heartbeat_onchannelcallback(void *context)
>  	}
>  }
>  
> +static int heartbeat_init(struct hv_util_service *srv)
> +{
> +	struct vmbus_channel *channel = srv->channel;
> +
> +	channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +
> +	return 0;
> +}
> +
>  #define HV_UTIL_RING_SEND_SIZE VMBUS_RING_SIZE(3 * HV_HYP_PAGE_SIZE)
>  #define HV_UTIL_RING_RECV_SIZE VMBUS_RING_SIZE(3 * HV_HYP_PAGE_SIZE)
>  
> @@ -734,6 +747,8 @@ static struct ptp_clock *hv_ptp_clock;
>  
>  static int hv_timesync_init(struct hv_util_service *srv)
>  {
> +	struct vmbus_channel *channel = srv->channel;
> +
>  	spin_lock_init(&host_ts.lock);
>  
>  	INIT_WORK(&adj_time_work, hv_set_host_time);
> @@ -750,6 +765,8 @@ static int hv_timesync_init(struct hv_util_service *srv)
>  		hv_ptp_clock = NULL;
>  	}
>  
> +	channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index 23999df52739..ae4240777f7d 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -636,6 +636,8 @@ static int synthvid_connect_vsp(struct hv_device *hdev)
>  	struct hvfb_par *par = info->par;
>  	int ret;
>  
> +	hdev->channel->max_pkt_size = HV_HYP_PAGE_SIZE + MAX_VMBUS_PKT_SIZE;
> +
>  	ret = vmbus_open(hdev->channel, RING_BUFSIZE, RING_BUFSIZE,
>  			 NULL, 0, synthvid_receive, hdev);
>  	if (ret) {
> -- 
> 2.34.1
>