linux-kernel - Re: Problems with csum_partial with misaligned buffers on sh4 platform

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Date: Sat, 10 Feb 2024 13:54:07 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc: Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: Problems with csum_partial with misaligned buffers on sh4
 platform

Hi Adrian,

On 2/10/24 12:12, John Paul Adrian Glaubitz wrote:
> Hi Guenter,
> 
> On Sat, 2024-02-10 at 07:12 -0800, Guenter Roeck wrote:
>> when running checksum unit tests on sh4 qemu emulations, I get the following
>> errors.
>>
>>      KTAP version 1
>>      # Subtest: checksum
>>      # module: checksum_kunit
>>      1..5
>>      # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_kunit.c:500
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 53378 (0xd082)
>>          ( u64)expec == 33488 (0x82d0)
>>      not ok 1 test_csum_fixed_random_inputs
>>      # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:525
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 65281 (0xff01)
>>          ( u64)expec == 65280 (0xff00)
>>      not ok 2 test_csum_all_carry_inputs
>>      # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:573
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 65535 (0xffff)
>>          ( u64)expec == 65534 (0xfffe)
>>      not ok 3 test_csum_no_carry_inputs
>>      ok 4 test_ip_fast_csum
>>      ok 5 test_csum_ipv6_magic
>> # checksum: pass:2 fail:3 skip:0 total:5
>>
>> The above is with from a little endian system. On a big endian system,
>> the test result is as follows.
>>
>>      KTAP version 1
>>      # Subtest: checksum
>>      # module: checksum_kunit
>>      1..5
>>      # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_kunit.c:500
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 33488 (0x82d0)
>>          ( u64)expec == 53378 (0xd082)
>>      not ok 1 test_csum_fixed_random_inputs
>>      # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:525
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 65281 (0xff01)
>>          ( u64)expec == 255 (0xff)
>>      not ok 2 test_csum_all_carry_inputs
>>      # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:565
>>      Expected ( u64)result == ( u64)expec, but
>>          ( u64)result == 1020 (0x3fc)
>>          ( u64)expec == 0 (0x0)
>>      not ok 3 test_csum_no_carry_inputs
>>      # test_ip_fast_csum: ASSERTION FAILED at lib/checksum_kunit.c:589
>>      Expected ( u64)expected == ( u64)csum_result, but
>>          ( u64)expected == 55939 (0xda83)
>>          ( u64)csum_result == 33754 (0x83da)
>>      not ok 4 test_ip_fast_csum
>>      # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:617
>>      Expected ( u64)expected_csum_ipv6_magic[i] == ( u64)csum_ipv6_magic(saddr, daddr, len, proto, csum), but
>>          ( u64)expected_csum_ipv6_magic[i] == 6356 (0x18d4)
>>          ( u64)csum_ipv6_magic(saddr, daddr, len, proto, csum) == 43586 (0xaa42)
>>      not ok 5 test_csum_ipv6_magic
>> # checksum: pass:0 fail:5 skip:0 total:5
>>
>> Note that test_ip_fast_csum and test_csum_ipv6_magic fail on all big endian
>> systems due to a bug in the test code, unrelated to this problem.
>>
>> Analysis shows that the errors are seen only if the buffer is misaligned.
>> Looking into arch/sh/lib/checksum.S, I found commit cadc4e1a2b4d2 ("sh:
>> Handle calling csum_partial with misaligned data") which seemed to be
>> related. Reverting that commit fixes the problem.
>> This suggests that something may be wrong with that commit. Alternatively,
>> of course, it may be possible that something is wrong with the qemu
>> emulation, but that seems unlikely.
> 
> I have not run these tests before. Can you tell me how these are run,
> so I can verify these reproduce on real hardware?
> 

Enabling CONFIG_KUNIT and CONFIG_CHECKSUM_KUNIT on top of a working
configuration should do the trick. Both can be built as module,
so presumably one can build and load them separately. I have not tried
that, though - I always build them into the kernel and boot the resulting
image.

Hope this helps,
Guenter