On 8/10/2025 4:48 AM, Puranjay Mohan wrote:
Changes in v1->v2: v1: https://lore.kernel.org/bpf/20250724125443.26182-1-puranjay@xxxxxxxxxx/ - Added comment in arch_bpf_timed_may_goto() about BPF_REG_FP setup (Xu Kuohai) This set adds support for the timed may_goto instruction for the arm64. The timed may_goto instruction is implemented by the verifier by reserving 2 8byte slots in the program stack and then calling arch_bpf_timed_may_goto() in a loop with the stack offset of these two slots in BPF_REG_AX. It expects the function to put a timestamp in the first slot and the returned count in BPF_REG_AX is put into the second slot by a store instruction emitted by the verifier. arch_bpf_timed_may_goto() is special as it receives the parameter in BPF_REG_AX and is expected to return the result in BPF_REG_AX as well. It can't clobber any caller saved registers because verifier doesn't save anything before emitting the call. So, arch_bpf_timed_may_goto() is implemented in assembly so the exact registers that are stored/restored can be controlled (BPF caller saved registers here) and it also needs to take care of moving arguments and return values to and from BPF_REG_AX <-> arm64 R0. So, arch_bpf_timed_may_goto() acts as a trampoline to call bpf_check_timed_may_goto() which does the main logic of placing the timestamp and returning the count. All tests that use may_goto instruction pass after the changing some of them in patch 2 #404 stream_errors:OK [...] #406/2 stream_success/stream_cond_break:OK [...] #494/23 verifier_bpf_fastcall/may_goto_interaction_x86_64:SKIP #494/24 verifier_bpf_fastcall/may_goto_interaction_arm64:OK [...] #539/1 verifier_may_goto_1/may_goto 0:OK #539/2 verifier_may_goto_1/batch 2 of may_goto 0:OK #539/3 verifier_may_goto_1/may_goto batch with offsets 2/1/0:OK #539/4 verifier_may_goto_1/may_goto batch with offsets 2/0:OK #539 verifier_may_goto_1:OK #540/1 verifier_may_goto_2/C code with may_goto 0:OK #540 verifier_may_goto_2:OK Summary: 7/16 PASSED, 25 SKIPPED, 0 FAILED Puranjay Mohan (2): bpf, arm64: Add JIT support for timed may_goto selftests/bpf: Enable timed may_goto tests for arm64 arch/arm64/net/Makefile | 2 +- arch/arm64/net/bpf_jit_comp.c | 13 +++++- arch/arm64/net/bpf_timed_may_goto.S | 40 +++++++++++++++++++ .../testing/selftests/bpf/prog_tests/stream.c | 2 +- .../bpf/progs/verifier_bpf_fastcall.c | 27 ++++++++----- .../selftests/bpf/progs/verifier_may_goto_1.c | 34 +++------------- 6 files changed, 76 insertions(+), 42 deletions(-) create mode 100644 arch/arm64/net/bpf_timed_may_goto.S
For the series, Acked-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
