[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAHgaXdKEv8zt-pHUrDE9J3K_fY-+z9ctxP+YCBOiWm5TUusr7Q@mail.gmail.com>
Date: Wed, 24 May 2017 00:43:59 +0530
From: Shubham Bansal <illusionist.neo@...il.com>
To: Russell King - ARM Linux <linux@...linux.org.uk>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] RFC: arm: eBPF JIT compiler
Hi Russell,
On Wed, May 24, 2017 at 12:30 AM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> Hi,
>
> On Wed, May 24, 2017 at 12:03:53AM +0530, Shubham Bansal wrote:
>> The JIT compiler emits ARM 32 bit instructions. Currently, It supports
>> eBPF only. Classic BPF is supported because of the conversion by BPF
>> core.
>>
>> JIT is enabled with
>>
>> echo 1 > /proc/sys/net/core/bpf_jit_enable
>>
>> Constant Blinding can be enabled along with JIT using
>>
>> echo 1 > /proc/sys/net/core/bpf_jit_enable
>> echo 2 > /proc/sys/net/core/bpf_jit_harden
>>
>> See Documentation/networking/filter.txt for more information.
>> Tested on ARMv7 with CONFIG_FRAME_POINTER enabled.
>
> What is this patch actually doing?
This is the first implementation of eBPF JIT for ARM.
>
> The commit message doesn't describe what changes this patch is doing,
> and it needs to. Presumably, it's adding support for eBPF?
Apologies. I thought commit message was good enough to understand. I
will resend the patch if needed.
Although, Its an RFC. I am requesting the community for with testing
and suggestions.
>
> If that's so, doesn't it need to change us from selecting HAVE_CBPF_JIT
> to selecting HAVE_EBPF_JIT ?
This patch is only for comments and testing. I thought, KConfig
changes wouldn't be needed unless
the patch is accepted.
>
> What about cases where the frame pointer is not enabled?If that's
> not supported then shouldn't the Kconfig be adjusted? What about
> users who are using cBPF without the frame pointer enabled?
I have tested it with and without the frame pointer as indicated in
the results shown in the mail.
>
> I haven't been able to go through the patch analysing it fully, but
> what I have read doesn't give me any immediate concerns. Only one
> spelling mistake stood out.
>
> Some things that I'm wondering though - what about endian issues?
> LDRD, for example, takes two registers, in ARM mode, these registers
> must be an even-odd pair. The even register is loaded from at the
> lowest address, the odd register from the higher address. This means
> when loading a BE value, the most significant word is in the even
> numbered register and the least significant word is in the odd numbered
> register. For LE values, the even numbered register contains the least
> significant word. Are we properly handling issues like this in all
> places?
Actually I haven't tested it with BE but tested it LE as I wasn't able
to run qemu to test it properly for BE.
I request anyone who has information on how to test it to help me with it.
>
>> +static const u8 bpf2a32[][2] = {
>> + /* return value from in-kernel function, and exit value from eBPF */
>> + [BPF_REG_0] = {ARM_R1, ARM_R0},
>> + /* arguments from eBPF program to in-kernel function */
>> + [BPF_REG_1] = {ARM_R3, ARM_R2},
>> + /* Stored on stack scratch space */
>> + [BPF_REG_2] = {STACK_OFFSET(0), STACK_OFFSET(4)},
>> + [BPF_REG_3] = {STACK_OFFSET(8), STACK_OFFSET(12)},
>> + [BPF_REG_4] = {STACK_OFFSET(16), STACK_OFFSET(20)},
>> + [BPF_REG_5] = {STACK_OFFSET(24), STACK_OFFSET(28)},
>> + /* callee saved registers that in-kernel function will preserve */
>> + [BPF_REG_6] = {ARM_R5, ARM_R4},
>> + /* Stored on stack scratch space */
>> + [BPF_REG_7] = {STACK_OFFSET(32), STACK_OFFSET(36)},
>> + [BPF_REG_8] = {STACK_OFFSET(40), STACK_OFFSET(44)},
>> + [BPF_REG_9] = {STACK_OFFSET(48), STACK_OFFSET(52)},
>> + /* Read only Frame Pointer to access Stack */
>> + [BPF_REG_FP] = {STACK_OFFSET(56), STACK_OFFSET(60)},
>> + /* Temperory Register for internal BPF JIT, can be used
>
> "Temporary"
I will correct that right away.
Thanks for the suggestions Russell.
-Shubham
Powered by blists - more mailing lists