Kernel: hazard pointers questioned, RISC-V IOMMU, BPF and mm work

Kernel traffic focused on concurrency primitives, architecture IOMMU enablement, BPF memory footprint, and several memory-management cleanups, plus stable security backports. Maintainer pushback on hazard pointers sat alongside concrete progress on RISC-V virtualization paths and optional BTF loading.

Hazard-pointer RFC draws Linus scrutiny

Paul McKenney and Mathieu Desnoyers posted RFC v3 of a 28-patch series adding a simple hazard-pointer implementation and torture tests. Linus Torvalds questioned the real-world value of the approach in the linux-kernel discussion. Developers watching lockless concurrency options should note the maintainer skepticism around adoption.

RISC-V IOMMU enables MSI remapping, DMA and VFIO

A v6 series for iommu/riscv adds IMSIC MSI remapping together with iommufd support, turning on IOMMU_DMA and VFIO by default. The patches complete a practical virtualization and DMA stack for the architecture. RISC-V platform and hypervisor work depends on this landing cleanly.

vmlinux BTF becomes on-demand loadable module

A bpf-next series makes CONFIG_DEBUG_INFO_BTF tristate so the vmlinux BTF can ship as a loadable module instead of a built-in blob. Unused systems reclaim roughly 5.4 MB of memory. Memory-constrained and embedded deployments gain a clear footprint win when BTF is not required.

nf_tables use-after-free fix headed to stable trees

A use-after-free in nf_tables_netdev_event binding-chain handling is requested for backport to the 6.12, 6.6, and 6.1 stable kernels, with tested patches attached. The fix closes a netfilter UAF path on long-term releases. Operators running those trees should expect the update.

PMD-level swap entries for anonymous THPs

The resend of v7 (29 patches) introduces PMD-level swap entries so anonymous transparent huge pages can be swapped without splitting to PTEs. Preserving THP structure across reclaim avoids the cost of collapse and rebuild. Workloads that thrash anonymous memory under pressure are the direct beneficiaries.

Userland page-table freeing made RCU-safe

A v5 series converts remaining architectures to RCU-safe page-table freeing, drops MMU_GATHER_RCU_TABLE_FREE, and enables lockless RCU walks. The cleanup unifies the free path across the mm subsystem. Concurrent page-table walkers and simpler architecture code are the practical outcomes.

VMA flag semantics made explicit, VM_SPECIAL removed

A 40-patch v3 series refactors VMA flags to eliminate VM_SPECIAL and make flag semantics explicit, under mm maintainer review. Clearer rules reduce misuse in core mm and drivers. Subsystem authors who set or test VMA flags need to track the new model.

BPF verifier fix for rbtree callback frames

CVE-2026-98047 addresses a BPF verifier bypass in rbtree callbacks when static subprograms are used, by checking ancestor frames. The one-message announcement records the corrected verification path. BPF toolchain and security-sensitive kernel users require the fix.