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2015-04-29hv_netvsc: Fix a bug in netvsc_start_xmit()KY Srinivasan3-26/+7
Commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated memory allocation in the packet send path: "hv_netvsc: Eliminate memory allocation in the packet send path The network protocol used to communicate with the host is the remote ndis (rndis) protocol. We need to decorate each outgoing packet with a rndis header and additional rndis state (rndis per-packet state). To manage this state, we currently allocate memory in the transmit path. Eliminate this allocation by requesting additional head room in the skb." This commit introduced a bug since it did not account for the case if the skb was cloned. Fix this bug. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Tested-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-29hv_netvsc: introduce netif-msg into netvsc moduleSimon Xiao4-7/+31
1. Introduce netif-msg to netvsc to control debug logging output and keep msg_enable in netvsc_device_context so that it is kept persistently. 2. Only call dump_rndis_message() when NETIF_MSG_RX_ERR or above is specified in netvsc module debug param. In non-debug mode, in current code, dump_rndis_message() will not dump anything but it still initialize some local variables and process the switch logic which is unnecessary, especially in high network throughput situation. Signed-off-by: Simon Xiao <sixiao@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-14hv_netvsc: Implement partial copy into send bufferHaiyang Zhang3-19/+46
If remaining space in a send buffer slot is too small for the whole message, we only copy the RNDIS header and PPI data into send buffer, so we can batch one more packet each time. It reduces the vmbus per-message overhead. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-08hv_netvsc: try linearizing big SKBs before dropping themVitaly Kuznetsov1-5/+20
In netvsc_start_xmit() we can handle packets which are scattered around not more than MAX_PAGE_BUFFER_COUNT-2 pages. It is, however, easy to create a packet which is not big in size but occupies more pages (e.g. if it uses frags on compound pages boundaries). When we drop such packet it cases sender to try resending it but in most cases it will try resending the same packet which will also get dropped, this will cause the particular connection to stick. To solve the issue we can try linearizing skb. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-08hv_netvsc: use single existing drop path in netvsc_start_xmitVitaly Kuznetsov1-8/+6
... which validly uses dev_kfree_skb_any() instead of dev_kfree_skb(). Setting ret to -EFAULT and -ENOMEM have no real meaning here (we need to set it to anything but -EAGAIN) as we drop the packet and return NETDEV_TX_OK anyway. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-08hv_netvsc: Fix the packet free when it is in skb headroomHaiyang Zhang3-3/+6
In the two places changed, we now use netvsc_xmit_completion() which properly frees hv_netvsc_packet in or not in skb headroom. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-08hv_netvsc: Define a macro RNDIS_AND_PPI_SIZEHaiyang Zhang2-12/+9
The sum of RNDIS msg and PPI struct sizes is used in multiple places, so we define a macro for them. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-08hv_netvsc: Clean up two unused variablesHaiyang Zhang3-4/+0
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-31hv_netvsc: Eliminate memory allocation in the packet send pathKY Srinivasan4-22/+60
The network protocol used to communicate with the host is the remote ndis (rndis) protocol. We need to decorate each outgoing packet with a rndis header and additional rndis state (rndis per-packet state). To manage this state, we currently allocate memory in the transmit path. Eliminate this allocation by requesting additional head room in the skb. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-31hv_netvsc: Cleanup the test for freeing skb when we use sendbuf mechanismKY Srinivasan2-2/+2
In preparation for embedding the rndis state and other packet state into the skb, cleanup the test for freeing the skb. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-29hv_netvsc: remove vmbus_are_subchannels_present() in rndis_filter_device_add()Haiyang Zhang1-2/+0
The vmbus_are_subchannels_present() also involves opening the channels, which may be too early at this point. Checking for subchannels is not necessary here. So this patch removes it. Subchannels will be opened when offer messages arrive. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-29hv_netvsc: Implement batching in send bufferHaiyang Zhang4-47/+162
With this patch, we can send out multiple RNDIS data packets in one send buffer slot and one VMBus message. It reduces the overhead associated with VMBus messages. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-01hyperv: Implement netvsc_get_channels() ethool opAndrew Schwartzmeyer3-1/+20
This adds support for reporting the actual and maximum combined channels count of the hv_netvsc driver via 'ethtool --show-channels'. This required adding 'max_chn' to 'struct netvsc_device', and assigning it 'rsscap.num_recv_que' in 'rndis_filter_device_add'. Now we can access the combined maximum channel count via 'struct netvsc_device' in the ethtool callback. Signed-off-by: Andrew Schwartzmeyer <andrew@schwartzmeyer.com> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-02-06hyperv: fix sparse warningsLad, Prabhakar2-5/+6
this patch fixes following sparse warnings: netvsc.c:688:5: warning: symbol 'netvsc_copy_to_send_buf' was not declared. Should it be static? rndis_filter.c:627:5: warning: symbol 'rndis_filter_set_offload_params' was not declared. Should it be static? rndis_filter.c:702:5: warning: symbol 'rndis_filter_set_rss_param' was not declared. Should it be static? Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-02-06Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-3/+8
Conflicts: drivers/net/vxlan.c drivers/vhost/net.c include/linux/if_vlan.h net/core/dev.c The net/core/dev.c conflict was the overlap of one commit marking an existing function static whilst another was adding a new function. In the include/linux/if_vlan.h case, the type used for a local variable was changed in 'net', whereas the function got rewritten to fix a stacked vlan bug in 'net-next'. In drivers/vhost/net.c, Al Viro's iov_iter conversions in 'net-next' overlapped with an endainness fix for VHOST 1.0 in 'net'. In drivers/net/vxlan.c, vxlan_find_vni() added a 'flags' parameter in 'net-next' whereas in 'net' there was a bug fix to pass in the correct network namespace pointer in calls to this function. Signed-off-by: David S. Miller <davem@davemloft.net>
2015-02-01hyperv: Fix the error processing in netvsc_send()Haiyang Zhang1-3/+8
The existing code frees the skb in EAGAIN case, in which the skb will be retried from upper layer and used again. Also, the existing code doesn't free send buffer slot in error case, because there is no completion message for unsent packets. This patch fixes these problems. (Please also include this patch for stable trees. Thanks!) Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-28hyperv: match wait_for_completion_timeout return typeNicholas Mc Guire1-7/+12
return type of wait_for_completion_timeout is unsigned long not int, this patch just fixes up the declarations. Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-28hyperv: netvsc.c: match wait_for_completion_timeout return typeNicholas Mc Guire1-2/+3
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-23hyperv: Fix some variable name typos in send-buffer init/revokeHaiyang Zhang2-7/+9
The changed names are union fields with the same size, so the existing code still works. But, we now update these variables to the correct names. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-09hyperv: Add support for vNIC hot removalHaiyang Zhang2-0/+6
This patch adds proper handling of the vNIC hot removal event, which includes a rescind-channel-offer message from the host side that triggers vNIC close and removal. In this case, the notices to the host during close and removal is not necessary because the channel is rescinded. This patch blocks these unnecessary messages, and lets vNIC removal process complete normally. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-11-26net: Hyper-V: Deletion of an unnecessary check before the function call "vfree"Markus Elfring1-3/+1
The vfree() function performs also input parameter validation. Thus the test around the call is not needed. This issue was detected by using the Coccinelle software. Signed-off-by: Markus Elfring <elfring@users.sourceforge.net> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-11-13hyperv: Add processing of MTU reduced by the hostHaiyang Zhang3-3/+14
If the host uses packet encapsulation feature, the MTU may be reduced by the host due to headroom reservation for encapsulation. This patch handles this new MTU value. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-30hyperv: Add IPv6 into the hash computation for vRSSHaiyang Zhang2-2/+5
This will allow the workload spreading via vRSS for IPv6. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-23hyperv: Fix the total_data_buflen in send pathHaiyang Zhang1-0/+1
total_data_buflen is used by netvsc_send() to decide if a packet can be put into send buffer. It should also include the size of RNDIS message before the Ethernet frame. Otherwise, a messge with total size bigger than send_section_size may be copied into the send buffer, and cause data corruption. [Request to include this patch to the Stable branches] Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-18hyperv: Add handling of IP header with option field in netvsc_set_hash()Haiyang Zhang1-16/+10
In case that the IP header has optional field at the end, this patch will get the port numbers after that field, and compute the hash. The general parser skb_flow_dissect() is used here. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-09Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-7/+8
2014-10-06hyperv: Fix a bug in netvsc_send()KY Srinivasan1-7/+8
After the packet is successfully sent, we should not touch the packet as it may have been freed. This patch is based on the work done by Long Li <longli@microsoft.com>. David, please queue this up for stable. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-02Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-1/+2
Conflicts: drivers/net/usb/r8152.c net/netfilter/nfnetlink.c Both r8152 and nfnetlink conflicts were simple overlapping changes. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30hyperv: Fix a bug in netvsc_start_xmit()KY Srinivasan1-1/+2
After the packet is successfully sent, we should not touch the skb as it may have been freed. This patch is based on the work done by Long Li <longli@microsoft.com>. In this version of the patch I have fixed issues pointed out by David. David, please queue this up for stable. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Tested-by: Long Li <longli@microsoft.com> Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-06hyperv: NULL dereference on errorDan Carpenter1-4/+2
We try to call free_netvsc_device(net_device) when "net_device" is NULL. It leads to an Oops. Fixes: f90251c8a6d0 ('hyperv: Increase the buffer length for netvsc_channel_cb()') Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-22hyperv: Increase the buffer length for netvsc_channel_cb()Haiyang Zhang2-4/+16
When the buffer is too small for a packet from VMBus, a bigger buffer will be allocated in netvsc_channel_cb() and retry reading the packet from VMBus. Increasing this buffer size will reduce the retry overhead. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-07hyperv: Adjust the size of sendbuf region to support ws2008r2KY Srinivasan1-1/+1
WS2008R2 is a supported platform and it turns out that the maximum sendbuf size that ws2008R2 can support is only 15MB. Make the necessary adjustment. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-05Drivers: net-next: hyperv: Increase the size of the sendbuf regionKY Srinivasan2-6/+3
Intel did some benchmarking on our network throughput when Linux on Hyper-V is as used as a gateway. This fix gave us almost a 1 Gbps additional throughput on about 5Gbps base throughput we hadi, prior to increasing the sendbuf size. The sendbuf mechanism is a copy based transport that we have which is clearly more optimal than the copy-free page flipping mechanism (for small packets). In the forwarding scenario, we deal only with MTU sized packets, and increasing the size of the senbuf area gave us the additional performance. For what it is worth, Windows guests on Hyper-V, I am told use similar sendbuf size as well. The exact value of sendbuf I think is less important than the fact that it needs to be larger than what Linux can allocate as physically contiguous memory. Thus the change over to allocating via vmalloc(). We currently allocate 16MB receive buffer and we use vmalloc there for allocation. Also the low level channel code has already been modified to deal with physically dis-contiguous memory in the ringbuffer setup. Based on experimentation Intel did, they say there was some improvement in throughput as the sendbuf size was increased up to 16MB and there was no effect on throughput beyond 16MB. Thus I have chosen 16MB here. Increasing the sendbuf value makes a material difference in small packet handling In this version of the patch, based on David's feedback, I have added additional details in the commit log. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-31Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-1/+3
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-24hyperv: Fix error return code in netvsc_init_buf()Wei Yongjun1-1/+3
Fix to return -ENOMEM from the kalloc error handling case instead of 0. Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn> Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-10hyperv: Add netpoll supportRichard Weinberger1-0/+11
In order to have at least a netconsole to debug kernel issues on Windows Azure this patch implements netpoll support. Sending packets is easy, netvsc_start_xmit() does already everything needed. Signed-off-by: Richard Weinberger <richard@nod.at> Acked-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-07-03drivers/net/hyperv/netvsc.c: remove unnecessary null test before kfreeFabian Frederick1-3/+1
Fix checkpatch warning: WARNING: kfree(NULL) is safe this check is probably not required Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: netdev@vger.kernel.org Signed-off-by: Fabian Frederick <fabf@skynet.be> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-26Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-1/+1
2014-06-20hyperv: Add handler for RNDIS_STATUS_NETWORK_CHANGE eventHaiyang Zhang3-25/+29
The RNDIS_STATUS_NETWORK_CHANGE event is received after the Hyper-V host sleep or hibernation. We refresh network at this time. MS-TFS: 135162 Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-06-17hyperv: fix apparent cut-n-paste error in send path teardownDave Jones1-1/+1
c25aaf814a63: "hyperv: Enable sendbuf mechanism on the send path" added some teardown code that looks like it was copied from the recieve path above, but missed a variable name replacement. Signed-off-by: Dave Jones <davej@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-23hyperv: Add hash value into RNDIS Per-packet infoHaiyang Zhang2-4/+18
It passes the hash value as the RNDIS Per-packet info to the Hyper-V host, so that the send completion notices can be spread across multiple channels. MS-TFS: 140273 Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-14net: get rid of SET_ETHTOOL_OPSWilfried Klaebe1-1/+1
net: get rid of SET_ETHTOOL_OPS Dave Miller mentioned he'd like to see SET_ETHTOOL_OPS gone. This does that. Mostly done via coccinelle script: @@ struct ethtool_ops *ops; struct net_device *dev; @@ - SET_ETHTOOL_OPS(dev, ops); + dev->ethtool_ops = ops; Compile tested only, but I'd seriously wonder if this broke anything. Suggested-by: Dave Miller <davem@davemloft.net> Signed-off-by: Wilfried Klaebe <w-lkml@lebenslange-mailadresse.de> Acked-by: Felipe Balbi <balbi@ti.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-12Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-0/+4
Conflicts: drivers/net/ethernet/altera/altera_sgdma.c net/netlink/af_netlink.c net/sched/cls_api.c net/sched/sch_api.c The netlink conflict dealt with moving to netlink_capable() and netlink_ns_capable() in the 'net' tree vs. supporting 'tc' operations in non-init namespaces. These were simple transformations from netlink_capable to netlink_ns_capable. The Altera driver conflict was simply code removal overlapping some void pointer cast cleanups in net-next. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-12Add support for netvsc build without CONFIG_SYSFS flagHaiyang Zhang1-4/+1
This change ensures the driver can be built successfully without the CONFIG_SYSFS flag. MS-TFS: 182270 Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-01hyperv: Properly handle checksum offloadKY Srinivasan1-0/+4
Do checksum offload only if the client of the driver wants checksum to be offloaded. In V1 version of this patch, I addressed comments from Stephen Hemminger <stephen@networkplumber.org> and Eric Dumazet <eric.dumazet@gmail.com>. In this version of the patch I have addressed comments from David Miller. This patch fixes a bug that is exposed in gateway scenarios. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-30hyperv: Enable sendbuf mechanism on the send pathKY Srinivasan3-9/+234
We send packets using a copy-free mechanism (this is the Guest to Host transport via VMBUS). While this is obviously optimal for large packets, it may not be optimal for small packets. Hyper-V host supports a second mechanism for sending packets that is "copy based". We implement that mechanism in this patch. In this version of the patch I have addressed a comment from David Miller. With this patch (and all of the other offload and VRSS patches), we are now able to almost saturate a 10G interface between Linux VMs on Hyper-V on different hosts - close to 9 Gbps as measured via iperf. Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-23hyperv: Simplify the send_completion variablesHaiyang Zhang4-16/+11
The union contains only one member now, so we use the variables in it directly. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-23hyperv: Remove recv_pkt_list and lockHaiyang Zhang4-198/+13
Removed recv_pkt_list and lock, and updated related code, so that the locking overhead is reduced especially when multiple channels are in use. The recv_pkt_list isn't actually necessary because the packets are processed sequentially in each channel. It has been replaced by a local variable, and the related lock for this list is also removed. The is_data_pkt field is not used in receive path, so its assignment is cleaned up. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-21hyperv: Add support for virtual Receive Side Scaling (vRSS)Haiyang Zhang4-34/+504
This feature allows multiple channels to be used by each virtual NIC. It is available on Hyper-V host 2012 R2. Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-11Drivers: net: hyperv: Address UDP checksum issuesKY Srinivasan3-2/+37
ws2008r2 does not support UDP checksum offload. Thus, we cannnot turn on UDP offload in the host. Also, on ws2012 and ws2012 r2, there appear to be an issue with UDP checksum offload. Fix this issue by computing the UDP checksum in the Hyper-V driver. Based on Dave Miller's comments, in this version, I have COWed the skb before modifying the UDP header (the checksum field). Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>