Status of the patches ===================== This patchset is currently incomplete: it oughtn't be released as-is, because that would necessitate incrementing architecture version number for a partial feature-set. However I've implemented the parts that I think are most interesting/controversial, so I'd like to get the review started. The missing elements that I'm aware of are: * Atomic subtract * Atomic & and | * Documentation updates The prog_test that's added depends on Clang/LLVM features added by Yonghong in https://reviews.llvm.org/D72184 This only includes a JIT implementation for x86_64 - I don't plan to implement JIT support myself for other architectures. Operations ========== This patchset adds atomic operations to the eBPF instruction set. The use-case that motivated this work was a trivial and efficient way to generate globally-unique cookies in BPF progs, but I think it's obvious that these features are pretty widely applicable. The instructions that are added here can be summarised with this list of kernel operations: * atomic[64]_[fetch_]add * atomic[64]_[fetch_]sub (TODO) * atomic[64]_[fetch_]and (TODO) * atomic[64]_[fetch_]or (TODO) * atomic[64]_xchg * atomic[64]_cmpxchg The following are left out of scope for this effort: * 16 and 8 bit operations * Explicit memory barriers Encoding ======== I originally planned to add new values for bpf_insn.opcode. This was rather unpleasant: the opcode space has holes in it but no entire instruction classes[1]. Yonghong Song had a better idea: use the immediate field of the existing STX XADD instruction to encode the operation. This works nicely, without breaking existing programs, because the immediate field is currently reserved-must-be-zero, and extra-nicely because BPF_ADD happens to be zero. Note that this of course makes immediate-source atomic operations impossible. It's hard to imagine a measurable speedup from such instructions, and if it existed it would certainly not benefit x86, which has no support for them. The BPF_OP opcode fields are re-used in the immediate, and an additional flag BPF_FETCH is used to mark instructions that should fetch a pre-modification value from memory. So, BPF_XADD is now called BPF_ATOMIC (the old name is kept to avoid breaking userspace builds), and where we previously had .imm = 0, we now have .imm = BPF_ADD (which is 0). Operands ======== Reg-source eBPF instructions only have two operands, while these atomic operations have up to four. To avoid needing to encode additional operands, then: - One of the input registers is re-used as an output register (e.g. atomic_fetch_add both reads from and writes to the source register). - Where necessary (i.e. for cmpxchg) , R0 is "hard-coded" as one of the operands. This approach also allows the new eBPF instructions to map directly to single x86 instructions. [1] Visualisation of eBPF opcode space: https://gist.github.com/bjackman/00fdad2d5dfff601c1918bc29b16e778 Brendan Jackman (7): bpf: Factor out emission of ModR/M for *(reg + off) bpf: x86: Factor out emission of REX byte bpf: Rename BPF_XADD and prepare to encode other atomics in .imm bpf: Move BPF_STX reserved field check into BPF_STX verifier code bpf: Add BPF_FETCH field / create atomic_fetch_add instruction bpf: Add instructions for atomic_cmpxchg and friends bpf: Add tests for new BPF atomic operations Documentation/networking/filter.rst | 27 ++-- arch/arm/net/bpf_jit_32.c | 7 +- arch/arm64/net/bpf_jit_comp.c | 16 +- arch/mips/net/ebpf_jit.c | 11 +- arch/powerpc/net/bpf_jit_comp64.c | 25 ++- arch/riscv/net/bpf_jit_comp32.c | 20 ++- arch/riscv/net/bpf_jit_comp64.c | 16 +- arch/s390/net/bpf_jit_comp.c | 26 ++-- arch/sparc/net/bpf_jit_comp_64.c | 14 +- arch/x86/net/bpf_jit_comp.c | 131 ++++++++++------ arch/x86/net/bpf_jit_comp32.c | 6 +- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 14 +- drivers/net/ethernet/netronome/nfp/bpf/main.h | 4 +- .../net/ethernet/netronome/nfp/bpf/verifier.c | 13 +- include/linux/filter.h | 47 +++++- include/uapi/linux/bpf.h | 9 +- kernel/bpf/core.c | 64 ++++++-- kernel/bpf/disasm.c | 25 ++- kernel/bpf/verifier.c | 72 ++++++--- lib/test_bpf.c | 2 +- samples/bpf/bpf_insn.h | 4 +- samples/bpf/sock_example.c | 3 +- samples/bpf/test_cgrp2_attach.c | 6 +- tools/include/linux/filter.h | 47 +++++- tools/include/uapi/linux/bpf.h | 9 +- tools/testing/selftests/bpf/Makefile | 2 +- .../selftests/bpf/prog_tests/atomics_test.c | 145 ++++++++++++++++++ .../bpf/prog_tests/cgroup_attach_multi.c | 6 +- .../selftests/bpf/progs/atomics_test.c | 61 ++++++++ .../selftests/bpf/verifier/atomic_cmpxchg.c | 96 ++++++++++++ .../selftests/bpf/verifier/atomic_fetch_add.c | 106 +++++++++++++ .../selftests/bpf/verifier/atomic_xchg.c | 113 ++++++++++++++ tools/testing/selftests/bpf/verifier/ctx.c | 6 +- .../testing/selftests/bpf/verifier/leak_ptr.c | 4 +- tools/testing/selftests/bpf/verifier/unpriv.c | 3 +- tools/testing/selftests/bpf/verifier/xadd.c | 2 +- 36 files changed, 1002 insertions(+), 160 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c -- 2.29.2.454.gaff20da3a2-goog
