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 15:52:50 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Daniel Borkmann <daniel@...earbox.net>,
        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 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>

> 
>>       default:
>>           pr_err("bpf_jit: unknown opcode %02x\n", code);
>>           return -EINVAL;
>>
> 

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/