Pu Lehui <pulehui@xxxxxxxxxx> writes: > On 2024/1/30 14:18, Björn Töpel wrote: >> Daniel Borkmann <daniel@xxxxxxxxxxxxx> writes: >> >>> On 1/29/24 10:13 AM, Pu Lehui wrote: >>>> On 2024/1/28 1:16, Björn Töpel wrote: >>>>> Pu Lehui <pulehui@xxxxxxxxxxxxxxx> writes: >>>>> >>>>>> From: Pu Lehui <pulehui@xxxxxxxxxx> >>>>>> >>>>>> Add necessary Zbb instructions introduced by [0] to reduce code size and >>>>>> improve performance of RV64 JIT. Meanwhile, a runtime deteted helper is >>>>>> added to check whether the CPU supports Zbb instructions. >>>>>> >>>>>> Link: https://github.com/riscv/riscv-bitmanip/releases/download/1.0.0/bitmanip-1.0.0-38-g865e7a7.pdf [0] >>>>>> Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx> >>>>>> --- >>>>>> arch/riscv/net/bpf_jit.h | 32 ++++++++++++++++++++++++++++++++ >>>>>> 1 file changed, 32 insertions(+) >>>>>> >>>>>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h >>>>>> index e30501b46f8f..51f6d214086f 100644 >>>>>> --- a/arch/riscv/net/bpf_jit.h >>>>>> +++ b/arch/riscv/net/bpf_jit.h >>>>>> @@ -18,6 +18,11 @@ static inline bool rvc_enabled(void) >>>>>> return IS_ENABLED(CONFIG_RISCV_ISA_C); >>>>>> } >>>>>> +static inline bool rvzbb_enabled(void) >>>>>> +{ >>>>>> + return IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && riscv_has_extension_likely(RISCV_ISA_EXT_ZBB); >>>>> >>>>> Hmm, I'm thinking about the IS_ENABLED(CONFIG_RISCV_ISA_ZBB) semantics >>>>> for a kernel JIT compiler. >>>>> >>>>> IS_ENABLED(CONFIG_RISCV_ISA_ZBB) affects the kernel compiler flags. >>>>> Should it be enough to just have the run-time check? Should a kernel >>>>> built w/o Zbb be able to emit Zbb from the JIT? >>>> >>>> Not enough, because riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) is >>>> a platform capability check, and the other one is a kernel image >>>> capability check. We can pass the check >>>> riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) when >>>> CONFIG_RISCV_ISA_ZBB=n. And my local test prove it. >> >> What I'm trying to say (and drew as well in the other reply) is that >> "riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) when >> CONFIG_RISCV_ISA_ZBB=n" should also make the JIT emit Zbb insns. The >> platform check should be sufficient. > > Ooh, this is really beyond my expectation. The test_progs can pass when > with only platform check and it can recognize the zbb instructions. Now > I know it. Sorry for misleading.🙁 > > Curious if CONFIG_RISCV_ISA_ZBB is still necessary? You don't need IS_ENABLED(CONFIG_RISCV_ISA_ZBB) for the JIT, but the kernel needs it. Feel free to follow up with a patch to remove it. Cheers, Björn
