linux-kernel - Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()

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Message-ID: <1ad358de-ac73-d430-aab1-c77df14b0011@microchip.com>
Date:   Mon, 4 Jul 2022 06:29:03 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <dlan@...too.org>, <mail@...chuod.ie>
CC:     <palmer@...belt.com>, <linux-riscv@...ts.infradead.org>,
        <paul.walmsley@...ive.com>, <aou@...s.berkeley.edu>,
        <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <kafai@...com>, <songliubraving@...com>, <yhs@...com>,
        <john.fastabend@...il.com>, <kpsingh@...nel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()

On 04/07/2022 03:20, Yixun Lan wrote:
> [You don't often get email from dlan@...too.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hi Conor Dooley:
> 
> On 14:12 Sun 03 Jul     , Conor Dooley wrote:
>> On 03/07/2022 14:09, Yixun Lan wrote:
>>> Enable this option to fix a bcc error in RISC-V platform
>>>
>>> And, the error shows as follows:
>>>
>>> ~ # runqlen
>>> WARNING: This target JIT is not designed for the host you are running. \
>>> If bad things happen, please choose a different -march switch.
>>> bpf: Failed to load program: Invalid argument
>>> 0: R1=ctx(off=0,imm=0) R10=fp0
>>> 0: (85) call bpf_get_current_task#35          ; R0_w=scalar()
>>> 1: (b7) r6 = 0                        ; R6_w=0
>>> 2: (7b) *(u64 *)(r10 -8) = r6         ; R6_w=P0 R10=fp0 fp-8_w=00000000
>>> 3: (07) r0 += 312                     ; R0_w=scalar()
>>> 4: (bf) r1 = r10                      ; R1_w=fp0 R10=fp0
>>> 5: (07) r1 += -8                      ; R1_w=fp-8
>>> 6: (b7) r2 = 8                        ; R2_w=8
>>> 7: (bf) r3 = r0                       ; R0_w=scalar(id=1) R3_w=scalar(id=1)
>>> 8: (85) call bpf_probe_read#4
>>> unknown func bpf_probe_read#4
>>> processed 9 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
>>>
>>> Traceback (most recent call last):
>>>    File "/usr/lib/python-exec/python3.9/runqlen", line 187, in <module>
>>>      b.attach_perf_event(ev_type=PerfType.SOFTWARE,
>>>    File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 1228, in attach_perf_event
>>>      fn = self.load_func(fn_name, BPF.PERF_EVENT)
>>>    File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 522, in load_func
>>>      raise Exception("Failed to load BPF program %s: %s" %
>>> Exception: Failed to load BPF program b'do_perf_event': Invalid argument
>>>
>>> Signed-off-by: Yixun Lan <dlan@...too.org>
>>
>> Do you know what commit this fixes?
>> Thanks,
>> Conor.
>>
> 
> I think this is effectively broken for RISC-V 64 at the commit:
>   0ebeea8ca8a4: bpf: Restrict bpf_probe_read{, str}() only to archs where they work
> 
> However, the bcc tools haven't got BPF support for RISC-V at that time,
> so no one noticed it
> 
> I can add a Fixes tag if you think it's a proper way

Hmm, I had a read of that commit and the breakage sounded intentional.
I ran a git log --grep "0ebeea8ca8a4" & it seems like a mixed bag of
fixes tags. Whether or not it deserves the explicit tag, mentioning
the commit would be useful. The tag would be:
Fixes: 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}() only to archs where they work")

Thanks,
Conor.

> 
>>> ---
>>>   arch/riscv/Kconfig | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index 32ffef9f6e5b4..da0016f1be6ce 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -25,6 +25,7 @@ config RISCV
>>>      select ARCH_HAS_GIGANTIC_PAGE
>>>      select ARCH_HAS_KCOV
>>>      select ARCH_HAS_MMIOWB
>>> +   select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>>>      select ARCH_HAS_PTE_SPECIAL
>>>      select ARCH_HAS_SET_DIRECT_MAP if MMU
>>>      select ARCH_HAS_SET_MEMORY if MMU
> 
> --
> Yixun Lan (dlan)
> Gentoo Linux Developer
> GPG Key ID AABEFD55
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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