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/admin-guide/mm/nommu-mmap.rst | 283 ++++++++++++++++++++++++++++ 1 file changed, 283 insertions(+) create mode 100644 Documentation/admin-guide/mm/nommu-mmap.rst (limited to 'Documentation/admin-guide/mm/nommu-mmap.rst') diff --git a/Documentation/admin-guide/mm/nommu-mmap.rst b/Documentation/admin-guide/mm/nommu-mmap.rst new file mode 100644 index 000000000..530fed08d --- /dev/null +++ b/Documentation/admin-guide/mm/nommu-mmap.rst @@ -0,0 +1,283 @@ +============================= +No-MMU memory mapping support +============================= + +The kernel has limited support for memory mapping under no-MMU conditions, such +as are used in uClinux environments. From the userspace point of view, memory +mapping is made use of in conjunction with the mmap() system call, the shmat() +call and the execve() system call. From the kernel's point of view, execve() +mapping is actually performed by the binfmt drivers, which call back into the +mmap() routines to do the actual work. + +Memory mapping behaviour also involves the way fork(), vfork(), clone() and +ptrace() work. Under uClinux there is no fork(), and clone() must be supplied +the CLONE_VM flag. + +The behaviour is similar between the MMU and no-MMU cases, but not identical; +and it's also much more restricted in the latter case: + + (#) Anonymous mapping, MAP_PRIVATE + + In the MMU case: VM regions backed by arbitrary pages; copy-on-write + across fork. + + In the no-MMU case: VM regions backed by arbitrary contiguous runs of + pages. + + (#) Anonymous mapping, MAP_SHARED + + These behave very much like private mappings, except that they're + shared across fork() or clone() without CLONE_VM in the MMU case. Since + the no-MMU case doesn't support these, behaviour is identical to + MAP_PRIVATE there. + + (#) File, MAP_PRIVATE, PROT_READ / PROT_EXEC, !PROT_WRITE + + In the MMU case: VM regions backed by pages read from file; changes to + the underlying file are reflected in the mapping; copied across fork. + + In the no-MMU case: + + - If one exists, the kernel will re-use an existing mapping to the + same segment of the same file if that has compatible permissions, + even if this was created by another process. + + - If possible, the file mapping will be directly on the backing device + if the backing device has the NOMMU_MAP_DIRECT capability and + appropriate mapping protection capabilities. Ramfs, romfs, cramfs + and mtd might all permit this. + + - If the backing device can't or won't permit direct sharing, + but does have the NOMMU_MAP_COPY capability, then a copy of the + appropriate bit of the file will be read into a contiguous bit of + memory and any extraneous space beyond the EOF will be cleared + + - Writes to the file do not affect the mapping; writes to the mapping + are visible in other processes (no MMU protection), but should not + happen. + + (#) File, MAP_PRIVATE, PROT_READ / PROT_EXEC, PROT_WRITE + + In the MMU case: like the non-PROT_WRITE case, except that the pages in + question get copied before the write actually happens. From that point + on writes to the file underneath that page no longer get reflected into + the mapping's backing pages. The page is then backed by swap instead. + + In the no-MMU case: works much like the non-PROT_WRITE case, except + that a copy is always taken and never shared. + + (#) Regular file / blockdev, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE + + In the MMU case: VM regions backed by pages read from file; changes to + pages written back to file; writes to file reflected into pages backing + mapping; shared across fork. + + In the no-MMU case: not supported. + + (#) Memory backed regular file, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE + + In the MMU case: As for ordinary regular files. + + In the no-MMU case: The filesystem providing the memory-backed file + (such as ramfs or tmpfs) may choose to honour an open, truncate, mmap + sequence by providing a contiguous sequence of pages to map. In that + case, a shared-writable memory mapping will be possible. It will work + as for the MMU case. If the filesystem does not provide any such + support, then the mapping request will be denied. + + (#) Memory backed blockdev, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE + + In the MMU case: As for ordinary regular files. + + In the no-MMU case: As for memory backed regular files, but the + blockdev must be able to provide a contiguous run of pages without + truncate being called. The ramdisk driver could do this if it allocated + all its memory as a contiguous array upfront. + + (#) Memory backed chardev, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE + + In the MMU case: As for ordinary regular files. + + In the no-MMU case: The character device driver may choose to honour + the mmap() by providing direct access to the underlying device if it + provides memory or quasi-memory that can be accessed directly. Examples + of such are frame buffers and flash devices. If the driver does not + provide any such support, then the mapping request will be denied. + + +Further notes on no-MMU MMAP +============================ + + (#) A request for a private mapping of a file may return a buffer that is not + page-aligned. This is because XIP may take place, and the data may not be + paged aligned in the backing store. + + (#) A request for an anonymous mapping will always be page aligned. If + possible the size of the request should be a power of two otherwise some + of the space may be wasted as the kernel must allocate a power-of-2 + granule but will only discard the excess if appropriately configured as + this has an effect on fragmentation. + + (#) The memory allocated by a request for an anonymous mapping will normally + be cleared by the kernel before being returned in accordance with the + Linux man pages (ver 2.22 or later). + + In the MMU case this can be achieved with reasonable performance as + regions are backed by virtual pages, with the contents only being mapped + to cleared physical pages when a write happens on that specific page + (prior to which, the pages are effectively mapped to the global zero page + from which reads can take place). This spreads out the time it takes to + initialize the contents of a page - depending on the write-usage of the + mapping. + + In the no-MMU case, however, anonymous mappings are backed by physical + pages, and the entire map is cleared at allocation time. This can cause + significant delays during a userspace malloc() as the C library does an + anonymous mapping and the kernel then does a memset for the entire map. + + However, for memory that isn't required to be precleared - such as that + returned by malloc() - mmap() can take a MAP_UNINITIALIZED flag to + indicate to the kernel that it shouldn't bother clearing the memory before + returning it. Note that CONFIG_MMAP_ALLOW_UNINITIALIZED must be enabled + to permit this, otherwise the flag will be ignored. + + uClibc uses this to speed up malloc(), and the ELF-FDPIC binfmt uses this + to allocate the brk and stack region. + + (#) A list of all the private copy and anonymous mappings on the system is + visible through /proc/maps in no-MMU mode. + + (#) A list of all the mappings in use by a process is visible through + /proc//maps in no-MMU mode. + + (#) Supplying MAP_FIXED or a requesting a particular mapping address will + result in an error. + + (#) Files mapped privately usually have to have a read method provided by the + driver or filesystem so that the contents can be read into the memory + allocated if mmap() chooses not to map the backing device directly. An + error will result if they don't. This is most likely to be encountered + with character device files, pipes, fifos and sockets. + + +Interprocess shared memory +========================== + +Both SYSV IPC SHM shared memory and POSIX shared memory is supported in NOMMU +mode. The former through the usual mechanism, the latter through files created +on ramfs or tmpfs mounts. + + +Futexes +======= + +Futexes are supported in NOMMU mode if the arch supports them. An error will +be given if an address passed to the futex system call lies outside the +mappings made by a process or if the mapping in which the address lies does not +support futexes (such as an I/O chardev mapping). + + +No-MMU mremap +============= + +The mremap() function is partially supported. It may change the size of a +mapping, and may move it [#]_ if MREMAP_MAYMOVE is specified and if the new size +of the mapping exceeds the size of the slab object currently occupied by the +memory to which the mapping refers, or if a smaller slab object could be used. + +MREMAP_FIXED is not supported, though it is ignored if there's no change of +address and the object does not need to be moved. + +Shared mappings may not be moved. Shareable mappings may not be moved either, +even if they are not currently shared. + +The mremap() function must be given an exact match for base address and size of +a previously mapped object. It may not be used to create holes in existing +mappings, move parts of existing mappings or resize parts of mappings. It must +act on a complete mapping. + +.. [#] Not currently supported. + + +Providing shareable character device support +============================================ + +To provide shareable character device support, a driver must provide a +file->f_op->get_unmapped_area() operation. The mmap() routines will call this +to get a proposed address for the mapping. This may return an error if it +doesn't wish to honour the mapping because it's too long, at a weird offset, +under some unsupported combination of flags or whatever. + +The driver should also provide backing device information with capabilities set +to indicate the permitted types of mapping on such devices. The default is +assumed to be readable and writable, not executable, and only shareable +directly (can't be copied). + +The file->f_op->mmap() operation will be called to actually inaugurate the +mapping. It can be rejected at that point. Returning the ENOSYS error will +cause the mapping to be copied instead if NOMMU_MAP_COPY is specified. + +The vm_ops->close() routine will be invoked when the last mapping on a chardev +is removed. An existing mapping will be shared, partially or not, if possible +without notifying the driver. + +It is permitted also for the file->f_op->get_unmapped_area() operation to +return -ENOSYS. This will be taken to mean that this operation just doesn't +want to handle it, despite the fact it's got an operation. For instance, it +might try directing the call to a secondary driver which turns out not to +implement it. Such is the case for the framebuffer driver which attempts to +direct the call to the device-specific driver. Under such circumstances, the +mapping request will be rejected if NOMMU_MAP_COPY is not specified, and a +copy mapped otherwise. + +.. important:: + + Some types of device may present a different appearance to anyone + looking at them in certain modes. Flash chips can be like this; for + instance if they're in programming or erase mode, you might see the + status reflected in the mapping, instead of the data. + + In such a case, care must be taken lest userspace see a shared or a + private mapping showing such information when the driver is busy + controlling the device. Remember especially: private executable + mappings may still be mapped directly off the device under some + circumstances! + + +Providing shareable memory-backed file support +============================================== + +Provision of shared mappings on memory backed files is similar to the provision +of support for shared mapped character devices. The main difference is that the +filesystem providing the service will probably allocate a contiguous collection +of pages and permit mappings to be made on that. + +It is recommended that a truncate operation applied to such a file that +increases the file size, if that file is empty, be taken as a request to gather +enough pages to honour a mapping. This is required to support POSIX shared +memory. + +Memory backed devices are indicated by the mapping's backing device info having +the memory_backed flag set. + + +Providing shareable block device support +======================================== + +Provision of shared mappings on block device files is exactly the same as for +character devices. If there isn't a real device underneath, then the driver +should allocate sufficient contiguous memory to honour any supported mapping. + + +Adjusting page trimming behaviour +================================= + +NOMMU mmap automatically rounds up to the nearest power-of-2 number of pages +when performing an allocation. This can have adverse effects on memory +fragmentation, and as such, is left configurable. The default behaviour is to +aggressively trim allocations and discard any excess pages back in to the page +allocator. In order to retain finer-grained control over fragmentation, this +behaviour can either be disabled completely, or bumped up to a higher page +watermark where trimming begins. + +Page trimming behaviour is configurable via the sysctl ``vm.nr_trim_pages``. -- cgit v1.2.3