Re: [PATCH 5/5] MIPS: Add support for eBPF JIT.

[David Daney]

On 05/26/2017 08:14 AM, Daniel Borkmann wrote:
> On 05/26/2017 02:38 AM, David Daney wrote:
> > Since the eBPF machine has 64-bit registers, we only support this in
> > 64-bit kernels.  As of the writing of this commit log test-bpf is 
> > showing:
> >
> >    test_bpf: Summary: 316 PASSED, 0 FAILED, [308/308 JIT'ed]
> >
> > All current test cases are successfully compiled.
> >
> > Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
>
> Awesome work!
>
> Did you also manage to run tools/testing/selftests/bpf/ fine with
> the JIT enabled?

I haven't done that yet, I will before the next revision.

> [...]
> > +struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> > +{
> > +    struct jit_ctx ctx;
> > +    unsigned int alloc_size;
> > +
> > +    /* Only 64-bit kernel supports eBPF */
> > +    if (!IS_ENABLED(CONFIG_64BIT) || !bpf_jit_enable)
>
> Isn't this already reflected by the following?
>
>    select HAVE_EBPF_JIT if (64BIT && !CPU_MICROMIPS)

Not exactly.  The eBPF JIT is in the same file as the classic-BPF JIT, 
so when HAVE_EBPF_JIT is false this will indeed never be called.  But 
the kernel would otherwise contain all the JIT code.

By putting in !IS_ENABLED(CONFIG_64BIT) we allow gcc to eliminate all 
the dead code when compiling the JITs.

> > +        return prog;
> > +
> > +    memset(&ctx, 0, sizeof(ctx));
> > +
> > +    ctx.offsets = kcalloc(prog->len + 1, sizeof(*ctx.offsets), 
> > GFP_KERNEL);
> > +    if (ctx.offsets == NULL)
> > +        goto out;
> > +
> > +    ctx.reg_val_types = kcalloc(prog->len + 1, 
> > sizeof(*ctx.reg_val_types), GFP_KERNEL);
> > +    if (ctx.reg_val_types == NULL)
> > +        goto out;
> > +
> > +    ctx.skf = prog;
> > +
> > +    if (reg_val_propagate(&ctx))
> > +        goto out;
> > +
> > +    /* First pass discovers used resources */
> > +    if (build_int_body(&ctx))
> > +        goto out;
> > +
> > +    /* Second pass generates offsets */
> > +    ctx.idx = 0;
> > +    if (gen_int_prologue(&ctx))
> > +        goto out;
> > +    if (build_int_body(&ctx))
> > +        goto out;
> > +    if (build_int_epilogue(&ctx))
> > +        goto out;
> > +
> > +    alloc_size = 4 * ctx.idx;
> > +
> > +    ctx.target = module_alloc(alloc_size);
>
> You would need to use bpf_jit_binary_alloc() like all other
> eBPF JITs do, otherwise kallsyms of the JITed progs would
> break.

OK, I was just copying code from the classic-BPF JIT in the same file. 
I will fix this.


> > +    if (ctx.target == NULL)
> > +        goto out;
> > +
> > +    /* Clean it */
> > +    memset(ctx.target, 0, alloc_size);
> > +
> > +    /* Third pass generates the code */
> > +    ctx.idx = 0;
> > +    if (gen_int_prologue(&ctx))
> > +        goto out;
> > +    if (build_int_body(&ctx))
> > +        goto out;
> > +    if (build_int_epilogue(&ctx))
> > +        goto out;
> > +    /* Update the icache */
> > +    flush_icache_range((ptr)ctx.target, (ptr)(ctx.target + ctx.idx));
> > +
> > +    if (bpf_jit_enable > 1)
> > +        /* Dump JIT code */
> > +        bpf_jit_dump(prog->len, alloc_size, 2, ctx.target);
> > +
> > +    prog->bpf_func = (void *)ctx.target;
> > +    prog->jited = 1;
> > +
> > +out:
> > +    kfree(ctx.offsets);
> > +    kfree(ctx.reg_val_types);
> > +
> > +    return prog;
> > +}