Thanks for taking a look!
On Fri, Sep 4, 2020 at 1:09 PM Andrii Nakryiko andrii.nakryiko@gmail.com wrote:
On Thu, Sep 3, 2020 at 3:35 PM Hao Luo haoluo@google.com wrote:
Add bpf_this_cpu_ptr() to help access percpu var on this cpu. This helper always returns a valid pointer, therefore no need to check returned value for NULL. Also note that all programs run with preemption disabled, which means that the returned pointer is stable during all the execution of the program.
Signed-off-by: Hao Luo haoluo@google.com
looks good, few small things, but otherwise:
Acked-by: Andrii Nakryiko andriin@fb.com
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/* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index d0ec94d5bdbf..e7ca91c697ed 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3612,6 +3612,19 @@ union bpf_attr {
bpf_per_cpu_ptr() must check the returned value.ReturnA generic pointer pointing to the kernel percpu variable on *cpu*.
- void *bpf_this_cpu_ptr(const void *percpu_ptr)
Description
Take a pointer to a percpu ksym, *percpu_ptr*, and return a
pointer to the percpu kernel variable on this cpu. See the
description of 'ksym' in **bpf_per_cpu_ptr**\ ().
bpf_this_cpu_ptr() has the same semantic as this_cpu_ptr() in
the kernel. Different from **bpf_per_cpu_ptr**\ (), it would
never return NULL.
Return
A generic pointer pointing to the kernel percpu variable onwhat's "a generic pointer"? is it as opposed to sk_buff pointer or something?
Ack. "A pointer" should be good enough. I wrote "generic pointer" because the per_cpu_ptr() in kernel code is a macro, whose returned value is a typed pointer, IIUC. But here we are missing the type. This is another difference between this helper and per_cpu_ptr(). But this may not matter.
/* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a702600ff581..e070d2abc405 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5016,8 +5016,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL; regs[BPF_REG_0].id = ++env->id_gen; regs[BPF_REG_0].mem_size = meta.mem_size;
} else if (fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL) {
} else if (fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL ||fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID) { const struct btf_type *t;bool not_null = fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID;nit: this is fine, but I'd inline it below
Ack.
mark_reg_known_zero(env, regs, BPF_REG_0); t = btf_type_skip_modifiers(btf_vmlinux, meta.ret_btf_id, NULL);@@ -5034,10 +5036,12 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn tname, PTR_ERR(ret)); return -EINVAL; }
regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
regs[BPF_REG_0].type = not_null ?PTR_TO_MEM : PTR_TO_MEM_OR_NULL; regs[BPF_REG_0].mem_size = tsize; } else {
regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;
regs[BPF_REG_0].type = not_null ?PTR_TO_BTF_ID : PTR_TO_BTF_ID_OR_NULL; regs[BPF_REG_0].btf_id = meta.ret_btf_id; } } else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index d474c1530f87..466acf82a9c7 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1160,6 +1160,18 @@ static const struct bpf_func_proto bpf_per_cpu_ptr_proto = { .arg2_type = ARG_ANYTHING, };
+BPF_CALL_1(bpf_this_cpu_ptr, const void *, percpu_ptr) +{
return (u64)this_cpu_ptr(percpu_ptr);see previous comment, this might trigger unnecessary compilation warnings on 32-bit arches
Ack. Will cast to "unsigned long". Thanks for catching this!
+}
+static const struct bpf_func_proto bpf_this_cpu_ptr_proto = {
.func = bpf_this_cpu_ptr,.gpl_only = false,.ret_type = RET_PTR_TO_MEM_OR_BTF_ID,.arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,+};
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