On 10/21/24 6:39 AM, Leon Hwang wrote:
In the x86_64 JIT, when calling a function, tailcall info is propagated if
the program is tail_call_reachable, regardless of whether the function is a
subprog, helper, or kfunc. However, this propagation is unnecessary for
not-tail_call_reachable subprogs, helpers, or kfuncs.
The verifier can determine if a subprog is tail_call_reachable. Therefore,
it can be optimized to only propagate tailcall info when the callee is
subprog and the subprog is actually tail_call_reachable.
Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
LGTM with a nit below.
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 4 +++-
kernel/bpf/verifier.c | 6 ++++++
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 06b080b61aa57..6ad6886ecfc88 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2124,10 +2124,12 @@ st: if (is_imm8(insn->off))
/* call */
case BPF_JMP | BPF_CALL: {
+ bool pseudo_call = src_reg == BPF_PSEUDO_CALL;
+ bool subprog_tail_call_reachable = dst_reg;
u8 *ip = image + addrs[i - 1];
func = (u8 *) __bpf_call_base + imm32;
- if (tail_call_reachable) {
+ if (pseudo_call && subprog_tail_call_reachable) {
LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
ip += 7;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f514247ba8ba8..6e7e42c7bc7b1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19990,6 +19990,12 @@ static int jit_subprogs(struct bpf_verifier_env *env)
insn[0].imm = (u32)addr;
insn[1].imm = addr >> 32;
}
+
+ if (bpf_pseudo_call(insn))
+ /* In the x86_64 JIT, tailcall information can only be
+ * propagated if the subprog is tail_call_reachable.
+ */
+ insn->dst_reg = env->subprog_info[subprog].tail_call_reachable;
The comment can be simplied as
/* Indicate whether callee is tail call
reachable or not */
}
err = bpf_prog_alloc_jited_linfo(prog);
