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

From: Daniel Borkmann <[email-masked]>
Date: Fri, 26 May 2017 17:35:09 +0200

On 05/26/2017 05:14 PM, 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 <[email-masked]>
>
> Awesome work!
>
> Did you also manage to run tools/testing/selftests/bpf/ fine with
> the JIT enabled?
>
> [...]
>> +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)

Oh, overlooked that you keep both JITs in the same file. ppc and
sparc also carry cBPF JITs, but strictly separated at compile time,
x86 threw out the cBPF one and only uses eBPF. Have you considered
separating them as well (which the current model assumes right now)?
(Need to double check all assumption we currently make and whether
they would still hold, but separation like all others do would
definitely be preferred.)

>> +        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.
>
>> +    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;
>> +}