linux-kernel - Re: [PATCH v2] loongarch/bpf: Skip speculation barrier opcode, which caused ltp testcase bpf

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Date:   Tue, 28 Mar 2023 10:37:36 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     WANG Xuerui <kernel@...0n.name>, George Guo <guodongtai@...inos.cn>
Cc:     ast@...nel.org, bpf@...r.kernel.org, chenhuacai@...nel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        loongarch@...ts.linux.dev, masahiroy@...nel.org,
        michal.lkml@...kovi.net, ndesaulniers@...gle.com,
        hengqi.chen@...il.com, yangtiezhu@...ngson.cn,
        tangyouling@...ngson.cn
Subject: Re: [PATCH v2] loongarch/bpf: Skip speculation barrier opcode, which
 caused ltp testcase bpf_prog02 to fail

On 3/28/23 9:52 AM, WANG Xuerui wrote:
> On 2023/3/28 15:22, Daniel Borkmann wrote:
>> On 3/28/23 9:13 AM, George Guo wrote:
>>> Here just skip the opcode(BPF_ST | BPF_NOSPEC) that has no couterpart to the loongarch.
>>>
>>> <snip>
>>>
>>> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
>>> index 288003a9f0ca..d3c6b1c4ccbb 100644
>>> --- a/arch/loongarch/net/bpf_jit.c
>>> +++ b/arch/loongarch/net/bpf_jit.c
>>> @@ -1022,6 +1022,11 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
>>>           emit_atomic(insn, ctx);
>>>           break;
>>> +    /* Speculation barrier */
>>> +    case BPF_ST | BPF_NOSPEC:
>>> +        pr_info_once("bpf_jit: skip speculation barrier opcode %0x2x\n", code);
>>> +        break;
>>
>> Thanks that looks better. Question to LoongArch folks (Cc): There is no equivalent
>> to a speculation barrier here, correct? Either way, I think the pr_info_once() can
>> just be removed given there is little value for a users to have this in the kernel
>> log. I can take care of this while applying, that's fine.
> 
> I can confirm there's currently no speculation barrier equivalent on lonogarch. (Loongson says there are builtin mitigations for Spectre-V1 and V2 on their chips, and AFAIK efforts to port the exploits to mips/loongarch have all failed a few years ago.)
> 
> And yes I'd agree with removing the warning altogether. Thanks for the reviews!
> 
> Acked-by: WANG Xuerui <git@...0n.name>

Ok, sounds good. I've cleaned this up and applied to bpf tree. Thanks!

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=a6f6a95f25803500079513780d11a911ce551d76