From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- Documentation/networking/checksum-offloads.rst | 143 +++++++++++++++++++++++++ 1 file changed, 143 insertions(+) create mode 100644 Documentation/networking/checksum-offloads.rst (limited to 'Documentation/networking/checksum-offloads.rst') diff --git a/Documentation/networking/checksum-offloads.rst b/Documentation/networking/checksum-offloads.rst new file mode 100644 index 000000000..69b23cf68 --- /dev/null +++ b/Documentation/networking/checksum-offloads.rst @@ -0,0 +1,143 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================= +Checksum Offloads +================= + + +Introduction +============ + +This document describes a set of techniques in the Linux networking stack to +take advantage of checksum offload capabilities of various NICs. + +The following technologies are described: + +* TX Checksum Offload +* LCO: Local Checksum Offload +* RCO: Remote Checksum Offload + +Things that should be documented here but aren't yet: + +* RX Checksum Offload +* CHECKSUM_UNNECESSARY conversion + + +TX Checksum Offload +=================== + +The interface for offloading a transmit checksum to a device is explained in +detail in comments near the top of include/linux/skbuff.h. + +In brief, it allows to request the device fill in a single ones-complement +checksum defined by the sk_buff fields skb->csum_start and skb->csum_offset. +The device should compute the 16-bit ones-complement checksum (i.e. the +'IP-style' checksum) from csum_start to the end of the packet, and fill in the +result at (csum_start + csum_offset). + +Because csum_offset cannot be negative, this ensures that the previous value of +the checksum field is included in the checksum computation, thus it can be used +to supply any needed corrections to the checksum (such as the sum of the +pseudo-header for UDP or TCP). + +This interface only allows a single checksum to be offloaded. Where +encapsulation is used, the packet may have multiple checksum fields in +different header layers, and the rest will have to be handled by another +mechanism such as LCO or RCO. + +CRC32c can also be offloaded using this interface, by means of filling +skb->csum_start and skb->csum_offset as described above, and setting +skb->csum_not_inet: see skbuff.h comment (section 'D') for more details. + +No offloading of the IP header checksum is performed; it is always done in +software. This is OK because when we build the IP header, we obviously have it +in cache, so summing it isn't expensive. It's also rather short. + +The requirements for GSO are more complicated, because when segmenting an +encapsulated packet both the inner and outer checksums may need to be edited or +recomputed for each resulting segment. See the skbuff.h comment (section 'E') +for more details. + +A driver declares its offload capabilities in netdev->hw_features; see +Documentation/networking/netdev-features.rst for more. Note that a device +which only advertises NETIF_F_IP[V6]_CSUM must still obey the csum_start and +csum_offset given in the SKB; if it tries to deduce these itself in hardware +(as some NICs do) the driver should check that the values in the SKB match +those which the hardware will deduce, and if not, fall back to checksumming in +software instead (with skb_csum_hwoffload_help() or one of the +skb_checksum_help() / skb_crc32c_csum_help functions, as mentioned in +include/linux/skbuff.h). + +The stack should, for the most part, assume that checksum offload is supported +by the underlying device. The only place that should check is +validate_xmit_skb(), and the functions it calls directly or indirectly. That +function compares the offload features requested by the SKB (which may include +other offloads besides TX Checksum Offload) and, if they are not supported or +enabled on the device (determined by netdev->features), performs the +corresponding offload in software. In the case of TX Checksum Offload, that +means calling skb_csum_hwoffload_help(skb, features). + + +LCO: Local Checksum Offload +=========================== + +LCO is a technique for efficiently computing the outer checksum of an +encapsulated datagram when the inner checksum is due to be offloaded. + +The ones-complement sum of a correctly checksummed TCP or UDP packet is equal +to the complement of the sum of the pseudo header, because everything else gets +'cancelled out' by the checksum field. This is because the sum was +complemented before being written to the checksum field. + +More generally, this holds in any case where the 'IP-style' ones complement +checksum is used, and thus any checksum that TX Checksum Offload supports. + +That is, if we have set up TX Checksum Offload with a start/offset pair, we +know that after the device has filled in that checksum, the ones complement sum +from csum_start to the end of the packet will be equal to the complement of +whatever value we put in the checksum field beforehand. This allows us to +compute the outer checksum without looking at the payload: we simply stop +summing when we get to csum_start, then add the complement of the 16-bit word +at (csum_start + csum_offset). + +Then, when the true inner checksum is filled in (either by hardware or by +skb_checksum_help()), the outer checksum will become correct by virtue of the +arithmetic. + +LCO is performed by the stack when constructing an outer UDP header for an +encapsulation such as VXLAN or GENEVE, in udp_set_csum(). Similarly for the +IPv6 equivalents, in udp6_set_csum(). + +It is also performed when constructing an IPv4 GRE header, in +net/ipv4/ip_gre.c:build_header(). It is *not* currently performed when +constructing an IPv6 GRE header; the GRE checksum is computed over the whole +packet in net/ipv6/ip6_gre.c:ip6gre_xmit2(), but it should be possible to use +LCO here as IPv6 GRE still uses an IP-style checksum. + +All of the LCO implementations use a helper function lco_csum(), in +include/linux/skbuff.h. + +LCO can safely be used for nested encapsulations; in this case, the outer +encapsulation layer will sum over both its own header and the 'middle' header. +This does mean that the 'middle' header will get summed multiple times, but +there doesn't seem to be a way to avoid that without incurring bigger costs +(e.g. in SKB bloat). + + +RCO: Remote Checksum Offload +============================ + +RCO is a technique for eliding the inner checksum of an encapsulated datagram, +allowing the outer checksum to be offloaded. It does, however, involve a +change to the encapsulation protocols, which the receiver must also support. +For this reason, it is disabled by default. + +RCO is detailed in the following Internet-Drafts: + +* https://tools.ietf.org/html/draft-herbert-remotecsumoffload-00 +* https://tools.ietf.org/html/draft-herbert-vxlan-rco-00 + +In Linux, RCO is implemented individually in each encapsulation protocol, and +most tunnel types have flags controlling its use. For instance, VXLAN has the +flag VXLAN_F_REMCSUM_TX (per struct vxlan_rdst) to indicate that RCO should be +used when transmitting to a given remote destination. -- cgit v1.2.3