Kernel: BPF unwind, RISC-V IOMMU, THP swap

BPF, memory management, and RISC-V IOMMU work led the day's kernel traffic, with several large revision series still under active review. Exception handling for BPF programs, huge-page swap retention, and VMA flag cleanup drew the heaviest discussion.

BPF exception cleanup landing pads

A v8 series of 22 patches on bpf-next implements exception cleanup landing pads that run when bpf_unwind() unwinds a program. The change is intended to support Rust panic paths and orderly resource release inside BPF. Developers building safer language runtimes on the verifier have a concrete path toward correct cleanup on unwind.

RISC-V IOMMU MSI remapping and VFIO

A v6 series of 16 patches enables IMSIC MSI remapping for the RISC-V IOMMU together with iommufd support. The work turns on IOMMU_DMA and VFIO by default. Virtualization and DMA isolation on RISC-V hardware move closer to parity with other architectures.

PMD-level swap entries for anonymous THPs

The v8 of a 30-patch mm series adds PMD-level swap entries so swapped anonymous transparent huge pages keep huge mappings across swap out and swap in instead of splitting to PTEs. Large-page workloads under reclaim pressure avoid the cost of repeated splits and rebuilds. Memory-management and performance-sensitive code that relies on THP should track the series.

AF_XDP zero-copy through page-pool providers

An RFC of 15 patches proposes integrating AF_XDP UMEM as a page-pool memory provider. The goal is to eliminate duplicated RX paths that page_pool drivers currently maintain. High-throughput XDP networking stacks stand to simplify their zero-copy receive paths if the approach lands.

Kernel support for rust-bpf programs

A v2 series of 15 patches from a maintainer adds kernel and libbpf support for BPF programs compiled by rustc. The patches introduce arena data sections and relaxed BTF rules. The work widens the set of languages that can produce verifier-accepted BPF objects.

MGLRU frequency-guided promotion

An RFC v3 series of 17 patches posts frequency-guided promotion changes for multi-generational LRU along with flag and ABI cleanups. The authors report 10-40 percent gains across their tests. Reclaim behavior and MGLRU users should watch whether the promotion heuristic holds up under broader review.

Explicit VMA flag semantics

A v3 series of 40 patches refactors mm VMA flags to make semantics explicit and to eliminate the overloaded VM_SPECIAL flag. The thread drew 191 messages and active review from mm maintainers. Code that inspects or sets VMA flags will eventually need to follow the clearer model.

secretmem regression with concurrent perf

A locked-vm accounting change for secretmem produces SIGBUS on memfd_secret() pages when perf record runs at the same time. Stable trees dropped the patch pending a perf-side fix. Users of confidential memory interfaces should treat the accounting path as temporarily rolled back.