Re: [PATCH v4 5/8] LoongArch: BPF: Don't assume trampoline size is page aligned

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On Wed, Sep 3, 2025 at 10:56 PM Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
>
> Hi, Hengqi,
>
> On Wed, Sep 3, 2025 at 8:06 PM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote:
> >
> > Currently, arch_alloc_bpf_trampoline() use bpf_prog_pack_alloc()
> > which will pack multiple trampolines into a huge page. So no need
> > to assume the trampoline size is page aligned.
> We do the alignment because larch_insn_text_copy() changes page attrs.
> If there is other data and BPF trampoline is in the same page,
> changing page attrs may cause errors.
>

Doesn't stop_machine() prevent this side effect?

> Huacai
>
> >
> > Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
> > ---
> >  arch/loongarch/net/bpf_jit.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> > index 35b13d91a979..43628b5e1553 100644
> > --- a/arch/loongarch/net/bpf_jit.c
> > +++ b/arch/loongarch/net/bpf_jit.c
> > @@ -1747,8 +1747,7 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> >
> >         ret = __arch_prepare_bpf_trampoline(&ctx, &im, m, tlinks, func_addr, flags);
> >
> > -       /* Page align */
> > -       return ret < 0 ? ret : round_up(ret * LOONGARCH_INSN_SIZE, PAGE_SIZE);
> > +       return ret < 0 ? ret : ret * LOONGARCH_INSN_SIZE;
> >  }
> >
> >  struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> > --
> > 2.43.5
> >





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