Kernel: BPF callx lands, hazard pointers, verifier and mm work

BPF development led the day as callx indirect subprogram calls reached bpf-next and related verifier and unwind series advanced, alongside hazard-pointer and scheduler proposals. Security backports closed a packet-pointer sign-extension hole and a tmpfs reference leak, while ext4 iomap conversion and hot-page tracking continued.

BPF callx enables indirect subprogram calls

A 17-patch series adding BPF callx, which performs indirect calls of BPF subprograms through function pointers, landed on bpf-next. The change requires JIT support and updates the verifier, liveness analysis, and call-graph handling. BPF developers gain a new calling model for programs that need function-pointer style indirection.

Hazard pointer updates under Linus review

A four-patch hazard pointer series was posted to the main kernel list. Linus Torvalds reviewed the ptr_eq implementation and address-dependency handling. The work matters for lock-free structures that depend on correct concurrent pointer lifetime rules.

BPF verifier blocks sign-extended packet pointers

A stable backport for 6.6.y makes the BPF verifier fail verification when packet data, data_end, or data_meta pointers are sign-extended. The fix addresses CVE-2024-47702. Operators on older kernels need the change to close the verifier hole.

tmpfs casefold unicode_map leak fixed

A patch corrects unicode_map reference-count leaks in tmpfs casefold option handling. The leak allowed an unprivileged local memory denial of service. Systems that enable casefold on tmpfs should take the fix.

BPF exception cleanup landing pads for bpf_unwind

Version 7 of a 22-patch series adds exception cleanup landing pads to the BPF verifier and JIT so bpf_unwind can run them safely. The series targets support for Rust panic paths in BPF programs. It strengthens exception semantics for the BPF runtime.

Steal governor and preferred CPUs merge to tip

Version 14 of the steal_governor series, introducing preferred CPUs and steal-driven vCPU backoff, was merged into tip/sched/core. The scheduler work targets virtualized hosts where steal time affects guest progress. Virtualization and scheduler developers gain new controls for vCPU behavior.

ext4 buffered I/O conversion to iomap continues

Version 6 of a 31-patch series moves ext4 regular-file buffered I/O from buffer_head to iomap. The patches address ordering, i_disksize, and data=ordered issues. Ext4 and storage developers should track the conversion for writeback correctness.

Hot-page tracking and promotion infrastructure

Version 8 of an eight-patch set introduces the pghot subsystem for unified hot-page tracking and asynchronous promotion on tiered memory such as DRAM plus CXL. Memory-management maintainers and reviewers are discussing the interfaces. Hosts with heterogeneous memory tiers stand to improve page placement.