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?
So if I understand you correctly, only relying on the
riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) part would not work -
iow, the IS_ENABLED(CONFIG_RISCV_ISA_ZBB) is mandatory here?
Thanks,
Daniel
P.s.: Given Bjorn's review and tests I took the series into bpf-next
now. Thanks everyone!
Thanks! Yes, this is mainly a semantic discussion, and it can be further
relaxed later with a follow up -- if applicable.
Björn
