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

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Message-ID: <e9c9348f-aa61-4384-e065-ba6bafc0bc13@caviumnetworks.com>
Date:   Fri, 26 May 2017 08:39:24 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        David Daney <david.daney@...ium.com>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
        ralf@...ux-mips.org
Cc:     Markos Chandras <markos.chandras@...tec.com>
Subject: Re: [PATCH 5/5] MIPS: Add support for eBPF JIT.

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@...ium.com>
> 
> 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;
>> +}
>