Re: [PATCH v2] loongarch/bpf: Skip speculation barrier opcode, which caused ltp testcase bpf_prog02 to fail

[WANG Xuerui]

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@xxxxxxxxxx>

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

--
WANG "xen0n" Xuerui

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