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

[Daniel Borkmann]

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@xxxxxxxxxx>

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