Public bug reported: [SRU Justification]
[Setup] - 2 or more QEMU Guest VMs sharing the the same host - the Guests are communicating using virtio-net-pci devices - vhost-net is enabled [Explanation] If one Guest VM sends GSO packets to another while GRO is disabled for receiver, so these packets are segmented by net/core. In this case, if zero-copy is enabled in vhost-net, the GSO packets TX completion is reported to userspace as before the TX is actually done. The vhost-net's zero-copy mechanism is enabled by default since v3.8-rc1 (f9611c43). [Impact] Incorrect/junk data sent in case the transmitting Guest OS re-uses/frees the TX buffer immediately upon TX completion. [Test Case] Windows 2008R2 Guest VMs running MS HCK Offload LSO test. NOTE1: GRO is always disabled in this case because it's not supported by Windows Guest virtio-net-pci drivers. NOTE2: MS HCK re-uses the GSO (LSO) buffers, so it reproduces the issue every time. [Note] This bug has been fixed in v3.14-rc7 by 1fd819ec (https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=1fd819ecb90cc9b822cd84d3056ddba315d3340f). The fix actually disables zero copy for this case since it forces unconditional fragments copying, but it resolves the issue mentioned. ** Affects: linux (Ubuntu) Importance: Undecided Status: Incomplete -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1328973 Title: GSO segmentation in zero-copy mode is broken Status in “linux” package in Ubuntu: Incomplete Bug description: [SRU Justification] [Setup] - 2 or more QEMU Guest VMs sharing the the same host - the Guests are communicating using virtio-net-pci devices - vhost-net is enabled [Explanation] If one Guest VM sends GSO packets to another while GRO is disabled for receiver, so these packets are segmented by net/core. In this case, if zero-copy is enabled in vhost-net, the GSO packets TX completion is reported to userspace as before the TX is actually done. The vhost-net's zero-copy mechanism is enabled by default since v3.8-rc1 (f9611c43). [Impact] Incorrect/junk data sent in case the transmitting Guest OS re-uses/frees the TX buffer immediately upon TX completion. [Test Case] Windows 2008R2 Guest VMs running MS HCK Offload LSO test. NOTE1: GRO is always disabled in this case because it's not supported by Windows Guest virtio-net-pci drivers. NOTE2: MS HCK re-uses the GSO (LSO) buffers, so it reproduces the issue every time. [Note] This bug has been fixed in v3.14-rc7 by 1fd819ec (https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=1fd819ecb90cc9b822cd84d3056ddba315d3340f). The fix actually disables zero copy for this case since it forces unconditional fragments copying, but it resolves the issue mentioned. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1328973/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
