kernel.git/Documentation/bpf, branch linux-6.15.y

bpf: Adjust free target to avoid global starvation of LRU map

2025-07-17T16:44:03Z

[ Upstream commit d4adf1c9ee7722545450608bcb095fb31512f0c6 ] BPF_MAP_TYPE_LRU_HASH can recycle most recent elements well before the map is full, due to percpu reservations and force shrink before neighbor stealing. Once a CPU is unable to borrow from the global map, it will once steal one elem from a neighbor and after that each time flush this one element to the global list and immediately recycle it. Batch value LOCAL_FREE_TARGET (128) will exhaust a 10K element map with 79 CPUs. CPU 79 will observe this behavior even while its neighbors hold 78 * 127 + 1 * 15 == 9921 free elements (99%). CPUs need not be active concurrently. The issue can appear with affinity migration, e.g., irqbalance. Each CPU can reserve and then hold onto its 128 elements indefinitely. Avoid global list exhaustion by limiting aggregate percpu caches to half of map size, by adjusting LOCAL_FREE_TARGET based on cpu count. This change has no effect on sufficiently large tables. Similar to LOCAL_NR_SCANS and lru->nr_scans, introduce a map variable lru->free_target. The extra field fits in a hole in struct bpf_lru. The cacheline is already warm where read in the hot path. The field is only accessed with the lru lock held. Tested-by: Anton Protopopov Signed-off-by: Willem de Bruijn Acked-by: Stanislav Fomichev Link: https://lore.kernel.org/r/20250618215803.3587312-1-willemdebruijn.kernel@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin

bpf: Add namespace to BPF internal symbols

2025-04-25T16:21:23Z

Add namespace to BPF internal symbols used by light skeleton to prevent abuse and document with the code their allowed usage. Fixes: b1d18a7574d0 ("bpf: Extend sys_bpf commands for bpf_syscall programs.") Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Acked-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/bpf/20250425014542.62385-1-alexei.starovoitov@gmail.com

bpf, docs: Fix broken link to renamed bpf_iter_task_vmas.c

2025-03-15T18:48:56Z

This file was renamed from bpf_iter_task_vma.c. Fixes: 45b38941c81f ("selftests/bpf: Rename bpf_iter_task_vma.c to bpf_iter_task_vmas.c") Signed-off-by: T.J. Mercier Acked-by: Song Liu Link: https://lore.kernel.org/r/20250304204520.201115-1-tjmercier@google.com Signed-off-by: Alexei Starovoitov

docs/bpf: Document some special sdiv/smod operations

2025-02-26T15:54:49Z

Patch [1] fixed possible kernel crash due to specific sdiv/smod operations in bpf program. The following are related operations and the expected results of those operations: - LLONG_MIN/-1 = LLONG_MIN - INT_MIN/-1 = INT_MIN - LLONG_MIN%-1 = 0 - INT_MIN%-1 = 0 Those operations are replaced with codes which won't cause kernel crash. This patch documents what operations may cause exception and what replacement operations are. [1] https://lore.kernel.org/all/20240913150326.1187788-1-yonghong.song@linux.dev/ Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20241107170924.2944681-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov

docs/bpf: Document the semantics of BTF tags with kind_flag

2025-02-06T00:17:59Z

Explain the meaning of kind_flag in BTF type_tags and decl_tags. Update uapi btf.h kind_flag comment to reflect the changes. Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250130201239.1429648-3-ihor.solodrai@linux.dev

bpf: Remove trailing whitespace in verifier.rst

2024-11-11T16:17:48Z

Remove trailing whitespace in Documentation/bpf/verifier.rst. Signed-off-by: Abhinav Saxena Link: https://lore.kernel.org/r/20241107063708.106340-2-xandfury@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko

docs/bpf: Add description of .BTF.base section

2024-10-29T20:15:36Z

Now that .BTF.base sections are generated for out-of-tree kernel modules (provided pahole supports the "distilled_base" BTF feature), document .BTF.base and its role in supporting resilient split BTF and BTF relocation. Changes since v1: - updated formatting, corrected typo, used BTF ID[s] consistently (Andrii) Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20241028091543.2175967-1-alan.maguire@oracle.com

docs/bpf: Add missing BPF program types to docs

2024-09-12T17:56:41Z

Update the table of program types in the libbpf documentation with the recently added program types. Signed-off-by: Donald Hunter Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240912095944.6386-1-donald.hunter@gmail.com

docs/bpf: Add constant values for linkages

2024-09-11T20:47:04Z

Make the values of the symbolic constants that define the valid linkages for functions and variables explicit. Signed-off-by: Will Hawkins Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20240911055033.2084881-1-hawkinsw@obs.cr

docs/bpf: Fix a typo in verifier.rst

2024-08-29T19:19:30Z

In verifier.rst, there is a typo in section 'Register parentage chains'. Caller saved registers are r0-r5, callee saved registers are r6-r9. Here by context it means callee saved registers rather than caller saved registers. This may confuse users. Signed-off-by: Yiming Xiang Link: https://lore.kernel.org/r/20240829031712.198489-1-kxiang@umich.edu Signed-off-by: Alexei Starovoitov