linux-kernel - Re: [PATCH bpf-next v1] bpf: Return -ENOTSUPP if callbacks are not allowed in non-JITed programs

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Message-ID: <0ea51d9f-7007-b893-0903-d9f76d6f34c9@loongson.cn>
Date: Thu, 4 Jan 2024 15:41:48 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: John Fastabend <john.fastabend@...il.com>,
 Eduard Zingerman <eddyz87@...il.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v1] bpf: Return -ENOTSUPP if callbacks are not
 allowed in non-JITed programs



On 01/03/2024 08:05 AM, John Fastabend wrote:
> Eduard Zingerman wrote:
>> On Mon, 2023-12-25 at 17:18 +0800, Tiezhu Yang wrote:
>>> If CONFIG_BPF_JIT_ALWAYS_ON is not set and bpf_jit_enable is 0, there
>>> exist 6 failed tests.

...

>>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>>> ---
>>>  kernel/bpf/verifier.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>> index a376eb609c41..1c780a893284 100644
>>> --- a/kernel/bpf/verifier.c
>>> +++ b/kernel/bpf/verifier.c
>>> @@ -19069,7 +19069,7 @@ static int fixup_call_args(struct bpf_verifier_env *env)
>>>  			 * have to be rejected, since interpreter doesn't support them yet.
>>>  			 */
>>>  			verbose(env, "callbacks are not allowed in non-JITed programs\n");
>>> -			return -EINVAL;
>>> +			return -ENOTSUPP;
>>>  		}
>>>
>>>  		if (!bpf_pseudo_call(insn))
>>
>> I agree with this change, however I think that it should be consistent.
>> Quick and non-exhaustive grepping shows that there are 4 places where
>> "non-JITed" is used in error messages: in check_map_func_compatibility()
>> and in fixup_call_args().
>> All these places currently use -EINVAL and should be updated to -ENOTSUPP,
>> if this change gets a green light.
>
> My preference is to just leave them as is unless its a serious
> problem. In this case any userspace has likely already figured
> out how to handle these errors so I don't think there is much
> value in changing things.

I am not quite sure whether to ignore this patch, but the state of
this patch is "Changes Requested" [1], I guess I should send v2 as
Eduard suggested.

[1] 
https://patchwork.kernel.org/project/netdevbpf/patch/20231225091830.6094-1-yangtiezhu@loongson.cn/

Thanks,
Tiezhu