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/driver-api/usb/persist.rst | 171 +++++++++++++++++++++++++++++++ 1 file changed, 171 insertions(+) create mode 100644 Documentation/driver-api/usb/persist.rst (limited to 'Documentation/driver-api/usb/persist.rst') diff --git a/Documentation/driver-api/usb/persist.rst b/Documentation/driver-api/usb/persist.rst new file mode 100644 index 000000000..08cafc629 --- /dev/null +++ b/Documentation/driver-api/usb/persist.rst @@ -0,0 +1,171 @@ +.. _usb-persist: + +USB device persistence during system suspend +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:Author: Alan Stern +:Date: September 2, 2006 (Updated February 25, 2008) + + +What is the problem? +==================== + +According to the USB specification, when a USB bus is suspended the +bus must continue to supply suspend current (around 1-5 mA). This +is so that devices can maintain their internal state and hubs can +detect connect-change events (devices being plugged in or unplugged). +The technical term is "power session". + +If a USB device's power session is interrupted then the system is +required to behave as though the device has been unplugged. It's a +conservative approach; in the absence of suspend current the computer +has no way to know what has actually happened. Perhaps the same +device is still attached or perhaps it was removed and a different +device plugged into the port. The system must assume the worst. + +By default, Linux behaves according to the spec. If a USB host +controller loses power during a system suspend, then when the system +wakes up all the devices attached to that controller are treated as +though they had disconnected. This is always safe and it is the +"officially correct" thing to do. + +For many sorts of devices this behavior doesn't matter in the least. +If the kernel wants to believe that your USB keyboard was unplugged +while the system was asleep and a new keyboard was plugged in when the +system woke up, who cares? It'll still work the same when you type on +it. + +Unfortunately problems _can_ arise, particularly with mass-storage +devices. The effect is exactly the same as if the device really had +been unplugged while the system was suspended. If you had a mounted +filesystem on the device, you're out of luck -- everything in that +filesystem is now inaccessible. This is especially annoying if your +root filesystem was located on the device, since your system will +instantly crash. + +Loss of power isn't the only mechanism to worry about. Anything that +interrupts a power session will have the same effect. For example, +even though suspend current may have been maintained while the system +was asleep, on many systems during the initial stages of wakeup the +firmware (i.e., the BIOS) resets the motherboard's USB host +controllers. Result: all the power sessions are destroyed and again +it's as though you had unplugged all the USB devices. Yes, it's +entirely the BIOS's fault, but that doesn't do _you_ any good unless +you can convince the BIOS supplier to fix the problem (lots of luck!). + +On many systems the USB host controllers will get reset after a +suspend-to-RAM. On almost all systems, no suspend current is +available during hibernation (also known as swsusp or suspend-to-disk). +You can check the kernel log after resuming to see if either of these +has happened; look for lines saying "root hub lost power or was reset". + +In practice, people are forced to unmount any filesystems on a USB +device before suspending. If the root filesystem is on a USB device, +the system can't be suspended at all. (All right, it _can_ be +suspended -- but it will crash as soon as it wakes up, which isn't +much better.) + + +What is the solution? +===================== + +The kernel includes a feature called USB-persist. It tries to work +around these issues by allowing the core USB device data structures to +persist across a power-session disruption. + +It works like this. If the kernel sees that a USB host controller is +not in the expected state during resume (i.e., if the controller was +reset or otherwise had lost power) then it applies a persistence check +to each of the USB devices below that controller for which the +"persist" attribute is set. It doesn't try to resume the device; that +can't work once the power session is gone. Instead it issues a USB +port reset and then re-enumerates the device. (This is exactly the +same thing that happens whenever a USB device is reset.) If the +re-enumeration shows that the device now attached to that port has the +same descriptors as before, including the Vendor and Product IDs, then +the kernel continues to use the same device structure. In effect, the +kernel treats the device as though it had merely been reset instead of +unplugged. + +The same thing happens if the host controller is in the expected state +but a USB device was unplugged and then replugged, or if a USB device +fails to carry out a normal resume. + +If no device is now attached to the port, or if the descriptors are +different from what the kernel remembers, then the treatment is what +you would expect. The kernel destroys the old device structure and +behaves as though the old device had been unplugged and a new device +plugged in. + +The end result is that the USB device remains available and usable. +Filesystem mounts and memory mappings are unaffected, and the world is +now a good and happy place. + +Note that the "USB-persist" feature will be applied only to those +devices for which it is enabled. You can enable the feature by doing +(as root):: + + echo 1 >/sys/bus/usb/devices/.../power/persist + +where the "..." should be filled in the with the device's ID. Disable +the feature by writing 0 instead of 1. For hubs the feature is +automatically and permanently enabled and the power/persist file +doesn't even exist, so you only have to worry about setting it for +devices where it really matters. + + +Is this the best solution? +========================== + +Perhaps not. Arguably, keeping track of mounted filesystems and +memory mappings across device disconnects should be handled by a +centralized Logical Volume Manager. Such a solution would allow you +to plug in a USB flash device, create a persistent volume associated +with it, unplug the flash device, plug it back in later, and still +have the same persistent volume associated with the device. As such +it would be more far-reaching than USB-persist. + +On the other hand, writing a persistent volume manager would be a big +job and using it would require significant input from the user. This +solution is much quicker and easier -- and it exists now, a giant +point in its favor! + +Furthermore, the USB-persist feature applies to _all_ USB devices, not +just mass-storage devices. It might turn out to be equally useful for +other device types, such as network interfaces. + + +WARNING: USB-persist can be dangerous!! +======================================= + +When recovering an interrupted power session the kernel does its best +to make sure the USB device hasn't been changed; that is, the same +device is still plugged into the port as before. But the checks +aren't guaranteed to be 100% accurate. + +If you replace one USB device with another of the same type (same +manufacturer, same IDs, and so on) there's an excellent chance the +kernel won't detect the change. The serial number string and other +descriptors are compared with the kernel's stored values, but this +might not help since manufacturers frequently omit serial numbers +entirely in their devices. + +Furthermore it's quite possible to leave a USB device exactly the same +while changing its media. If you replace the flash memory card in a +USB card reader while the system is asleep, the kernel will have no +way to know you did it. The kernel will assume that nothing has +happened and will continue to use the partition tables, inodes, and +memory mappings for the old card. + +If the kernel gets fooled in this way, it's almost certain to cause +data corruption and to crash your system. You'll have no one to blame +but yourself. + +For those devices with avoid_reset_quirk attribute being set, persist +maybe fail because they may morph after reset. + +YOU HAVE BEEN WARNED! USE AT YOUR OWN RISK! + +That having been said, most of the time there shouldn't be any trouble +at all. The USB-persist feature can be extremely useful. Make the +most of it. -- cgit v1.2.3