The first half of the 5.17 merge window

As of this writing, just short of 7,000 non-merge commits have been pulled into the mainline kernel repository for the 5.17 release. The changes pulled thus far bring new features across the kernel; read on for a summary of what has been merged during the first half of the 5.17 merge window.

Architecture-specific

• The arm64 architecture has gained support for the kernel concurrency sanitizer (KCSAN).
• 32-Bit Arm systems now support KFENCE.
• The boot-time memtest memory tester is now available on the m68k architecture.
• The new "AMD P-State" subsystem is a power-control mechanism for upcoming AMD processors that, it is said, offers significantly better performance. See this documentation commit for more information.

Core kernel

• The bpf_loop() helper is an alternative way of implementing (some) loops in BPF programs; it can improve performance and ease the task of getting loops past the BPF verifier.
• The "compile once/run everywhere" (CO-RE) mechanism, formerly implemented in user space, now runs within the kernel. This is a step toward the eventual implementation of signed BPF programs and also makes BPF functionality more readily available to languages like Go.
• The scheduler now tracks forced-idle time — the time that an SMT sibling processor is forced into the idle state as the result of core-scheduling constraints. This information, which can be used to evaluate the cost of enabling core scheduling, can be found in /proc/PID/sched.
• The RCU_FAST_NO_HZ configuration option, meant for advanced tweaking of the RCU algorithm on tickless CPUs, has been removed. It seems that no actual users of this feature could be found.

Filesystems and block I/O

• ID-mapped filesystem mounts can now be made on top of filesystems that are, themselves, ID-mapped. This merge commit has some more information.

Hardware support

• Graphics: the direct rendering subsystem has gained support for electronic privacy screens, as found on various laptop models. Also: JDI R63452 Full HD DSI panels, Ilitek ILI9163 display panels, Novatek NT35950 DSI panels, Boe BF060Y8M-AJ0 panels, Sony Tulip Truly NT35521 panels, and R-Car DU MIPI DSI encoders.
• Hardware monitoring: Texas Instruments INA238 power monitors, ASUS WMI B550/X570 and X370/X470/B450/X399 hardware monitoring interfaces, Delta AHE-50DC fan control modules, Renesas RZ/G2L thermal sensors, MPS MP5023 hardware monitoring interfaces, and NZXT fan controllers.
• Media: STMicroelectronics STM32 Chrom-Art accelerators, Maxim MAX96712 quad GMSL2 deserializers, OmniVision OV5693 sensors, and various codecs with VP9 support.
• Miscellaneous: Apple PMGR power-state controllers, R-Car Gen4 system controllers, Samsung Exynos universal serial interfaces, StarFive JH7100 clock generators, StarFive JH7100 reset controllers, Marvell CN10K performance-monitoring units, HiSilicon PCIe performance-monitoring units, Marvell CN10K random number generators, Letsketch WP9620N tablets, Maxim MAX77976 battery chargers, Lenovo Yoga Book tablets, Siemens Simatic LED controllers, Siemens Simatic IPC watchdogs, Asus TF103C 2-in-1 keyboard docks, Renesas R-Car Gen3 and RZ/N1 NAND controllers, TI TPS68470 PMIC regulators, and Maxim MAX20086-MAX20089 camera power protectors.
• Networking: Engleder TSN endpoint Ethernet MACs, Microchip Lan966x network switches, Vertexcom MSE102x SPI interfaces, and Mellanox Spectrum-4 Ethernet switches.
• Pin control: Qualcomm SDX65 and SM8450 pin controllers, StarFive JH7100 pin controllers, NXP IMXRT1050 pin controllers, and Intel Thunder Bay pin controllers.

Networking

• The reference-count tracking infrastructure has been added. This mechanism should help developers track down the source of reference-count bugs. For now it is specific to the networking subsystem but should be relatively easily extended to other parts of the kernel.
• The new "converged security and management engine" module allows communication with the Intel management engine (the separate processor lurking within Intel CPUs) via WiFi.
• Support for offloading traffic-control actions to network devices has been added; some information can be found in this commit.
• The management component transport protocol (MCTP) is now supported over serial devices. MCTP support over SMBus was also merged but subsequently reverted after the I2C maintainer complained about not having been involved in the necessary I2C core changes.

Security-related

• The kernel's random-number generator has switched from the SHA1 hash algorithm to BLAKE2s, which is both faster and more secure.

Virtualization and containers

• User-mode Linux can now be booted with a devicetree blob, facilitating testing of driver code.
• The Xen USB virtual host driver allows access to USB devices to be passed through to Xen guests.

Internal kernel changes

• The struct page fields used by the slab allocators have been moved into a separate structure. An early version of this work was covered in this article; it has since been pushed further by Vlastimil Babka.
• KCSAN has gained the ability to detect some missing memory barriers. Some more information can be found in this documentation commit.
• The new gpio-sim module creates simulated GPIO chips for testing; see this commit for more information.
• The kernel is now built with -Wcast-function-type, which generates a warning when function pointers are cast to an incompatible type. This check is necessary to avoid setting off control-flow integrity alarms.

There are currently about 4,000 changesets sitting in linux-next, suggesting that activity will be a bit slower for the rest of the merge window. That said, there are undoubtedly some interesting changes yet to land in the mainline; that should happen by the time the merge window closes on January 23. Stay tuned for our second-half summary, which will arrive shortly after that date.

Index entries for this article
Kernel	Releases/5.17

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