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Sender: Guenter Roeck <groeck7@gmail.com>
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Date: Mon, 22 Jan 2024 17:06:09 -0800
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Subject: Re: [PATCH v15 5/5] kunit: Add tests for csum_ipv6_magic and
 ip_fast_csum
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To: Charlie Jenkins <charlie@rivosinc.com>,
 Palmer Dabbelt <palmer@dabbelt.com>
Cc: David.Laight@aculab.com, Conor Dooley <conor@kernel.org>,
 samuel.holland@sifive.com, xiao.w.wang@intel.com,
 Evan Green <evan@rivosinc.com>, guoren@kernel.org,
 linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
 linux-arch@vger.kernel.org, Paul Walmsley <paul.walmsley@sifive.com>,
 aou@eecs.berkeley.edu, Arnd Bergmann <arnd@arndb.de>
References: <be959a4bb660466faba5ade7976485c8@AcuMS.aculab.com>
 <mhng-b5f26a34-7632-4423-9f07-3224170bae9f@palmer-ri-x1c9>
 <Za8AXnKCm4cPyVbp@ghost>
From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <Za8AXnKCm4cPyVbp@ghost>
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On 1/22/24 15:55, Charlie Jenkins wrote:
> On Mon, Jan 22, 2024 at 03:39:16PM -0800, Palmer Dabbelt wrote:
>> On Mon, 22 Jan 2024 13:41:48 PST (-0800), David.Laight@ACULAB.COM wrote:
>>> From: Guenter Roeck
>>>> Sent: 22 January 2024 17:16
>>>>
>>>> On 1/22/24 08:52, David Laight wrote:
>>>>> From: Guenter Roeck
>>>>>> Sent: 22 January 2024 16:40
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> On Mon, Jan 08, 2024 at 03:57:06PM -0800, Charlie Jenkins wrote:
>>>>>>> Supplement existing checksum tests with tests for csum_ipv6_magic and
>>>>>>> ip_fast_csum.
>>>>>>>
>>>>>>> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
>>>>>>> ---
>>>>>>
>>>>>> With this patch in the tree, the arm:mps2-an385 qemu emulation gets a bad hiccup.
>>>>>>
>>>>>> [    1.839556] Unhandled exception: IPSR = 00000006 LR = fffffff1
>>>>>> [    1.839804] CPU: 0 PID: 164 Comm: kunit_try_catch Tainted: G                 N 6.8.0-rc1 #1
>>>>>> [    1.839948] Hardware name: Generic DT based system
>>>>>> [    1.840062] PC is at __csum_ipv6_magic+0x8/0xb4
>>>>>> [    1.840408] LR is at test_csum_ipv6_magic+0x3d/0xa4
>>>>>> [    1.840493] pc : [<21212f34>]    lr : [<21117fd5>]    psr: 0100020b
>>>>>> [    1.840586] sp : 2180bebc  ip : 46c7f0d2  fp : 21275b38
>>>>>> [    1.840664] r10: 21276b60  r9 : 21275b28  r8 : 21465cfc
>>>>>> [    1.840751] r7 : 00003085  r6 : 21275b4e  r5 : 2138702c  r4 : 00000001
>>>>>> [    1.840847] r3 : 2c000000  r2 : 1ac7f0d2  r1 : 21275b39  r0 : 21275b29
>>>>>> [    1.840942] xPSR: 0100020b
>>>>>>
>>>>>> This translates to:
>>>>>>
>>>>>> PC is at __csum_ipv6_magic (arch/arm/lib/csumipv6.S:15)
>>>>>> LR is at test_csum_ipv6_magic (./arch/arm/include/asm/checksum.h:60
>>>>>> ./arch/arm/include/asm/checksum.h:163 lib/checksum_kunit.c:617)
>>>>>>
>>>>>> Obviously I can not say if this is a problem with qemu or a problem with
>>>>>> the Linux kernel. Given that, and the presumably low interest in
>>>>>> running mps2-an385 with Linux, I'll simply disable that test. Just take
>>>>>> it as a heads up that there _may_ be a problem with this on arm
>>>>>> nommu systems.
>>>>>
>>>>> Can you drop in a disassembly of __csum_ipv6_magic ?
>>>>> Actually I think it is:
>>>>
>>>> It is, as per the PC pointer above. I don't know anything about arm assembler,
>>>> much less about its behavior with THUMB code.
>>>
>>> Doesn't look like thumb to me (offset 8 is two 4-byte instructions) and
>>> the code I found looks like arm to me.
>>> (I haven't written any arm asm since before they invented thumb!)
>>>
>>>>> ENTRY(__csum_ipv6_magic)
>>>>> 		str	lr, [sp, #-4]!
>>>>> 		adds	ip, r2, r3
>>>>> 		ldmia	r1, {r1 - r3, lr}
>>>>>
>>>>> So the fault is (probably) a misaligned ldmia ?
>>>>> Are they ever supported?
>>>>>
>>>>
>>>> Good question. My primary guess is that this never worked. As I said,
>>>> this was just intended to be informational, (probably) no reason to bother.
>>>>
>>>> Of course one might ask if it makes sense to even keep the arm nommu code
>>>> in the kernel, but that is of course a different question. I do wonder though
>>>> if anyone but me is running it.
>>>
>>> If it is an alignment fault it isn't a 'nommu' bug.
>>>
>>> And traditionally arm didn't support misaligned transfers (well not
>>> in anyway any other cpu did!).
>>> It might be that the kernel assumes that all ethernet packets are
>>> aligned, but the test suite isn't aligning the buffer.
>>> Which would make it a test suite bug.
>>
>>  From talking to Evan and Vineet, I think you're right and this is a test
>> suite bug: specifically the tests weren't respecting NET_IP_ALIGN.  That
>> didn't crop up for ip_fast_csum() as it just uses ldr which supports
>> misaligned accesses on the M3 (at least as far as I can tell).
>>
>> So I think the right fix is something like
>>
>>     diff --git a/lib/checksum_kunit.c b/lib/checksum_kunit.c
>>     index 225bb7701460..2dd282e27dd4 100644
>>     --- a/lib/checksum_kunit.c
>>     +++ b/lib/checksum_kunit.c
>>     @@ -5,6 +5,7 @@
>>      #include <kunit/test.h>
>>      #include <asm/checksum.h>
>>     +#include <asm/checksum.h>
>>      #include <net/ip6_checksum.h>
>>      #define MAX_LEN 512
>>     @@ -15,6 +16,7 @@
>>      #define IPv4_MAX_WORDS 15
>>      #define NUM_IPv6_TESTS 200
>>      #define NUM_IP_FAST_CSUM_TESTS 181
>>     +#define SUPPORTED_ALIGNMENT (1 << NET_IP_ALIGN)
>>      /* Values for a little endian CPU. Byte swap each half on big endian CPU. */
>>      static const u32 random_init_sum = 0x2847aab;
>>     @@ -486,7 +488,7 @@ static void test_csum_fixed_random_inputs(struct kunit *test)
>>      	__sum16 result, expec;
>>      	assert_setup_correct(test);
>>     -	for (align = 0; align < TEST_BUFLEN; ++align) {
>>     +	for (align = 0; align < TEST_BUFLEN; align += SUPPORTED_ALIGNMENT) {
>>      		memcpy(&tmp_buf[align], random_buf,
>>      		       min(MAX_LEN, TEST_BUFLEN - align));
>>      		for (len = 0; len < MAX_LEN && (align + len) < TEST_BUFLEN;
>>     @@ -513,7 +515,7 @@ static void test_csum_all_carry_inputs(struct kunit *test)
>>      	assert_setup_correct(test);
>>      	memset(tmp_buf, 0xff, TEST_BUFLEN);
>>     -	for (align = 0; align < TEST_BUFLEN; ++align) {
>>     +	for (align = 0; align < TEST_BUFLEN; align += SUPPORTED_ALIGNMENT) {
>>      		for (len = 0; len < MAX_LEN && (align + len) < TEST_BUFLEN;
>>      		     ++len) {
>>      			/*
>>     @@ -553,7 +555,7 @@ static void test_csum_no_carry_inputs(struct kunit *test)
>>      	assert_setup_correct(test);
>>      	memset(tmp_buf, 0x4, TEST_BUFLEN);
>>     -	for (align = 0; align < TEST_BUFLEN; ++align) {
>>     +	for (align = 0; align < TEST_BUFLEN; align += SUPPORTED_ALIGNMENT) {
>>      		for (len = 0; len < MAX_LEN && (align + len) < TEST_BUFLEN;
>>      		     ++len) {
>>      			/*
>>
>> but I haven't even build tested it...
> 
> This doesn't fix the test_csum_ipv6_magic test case that was causing the
> initial problem, but the same trick can be done in that test.
> 

The above didn't (and still doesn't) fail for me. The following fixes the problem.
So, yes, I guess the problem has to do with alignment. I don't know if NET_IP_ALIGN
would do the trick, though - it works, but it seems to me that the definition of
NET_IP_ALIGN is supposed to address potential performance issues, not mandatory
IP header alignment.

Thanks,
Guenter

---
diff --git a/lib/checksum_kunit.c b/lib/checksum_kunit.c
index 225bb7701460..c8730af2a474 100644
--- a/lib/checksum_kunit.c
+++ b/lib/checksum_kunit.c
@@ -591,6 +591,8 @@ static void test_ip_fast_csum(struct kunit *test)
         }
  }

+#define SUPPORTED_ALIGNMENT (1 << NET_IP_ALIGN)
+
  static void test_csum_ipv6_magic(struct kunit *test)
  {
  #if defined(CONFIG_NET)
@@ -607,7 +609,7 @@ static void test_csum_ipv6_magic(struct kunit *test)
         const int csum_offset = sizeof(struct in6_addr) + sizeof(struct in6_addr) +
                             sizeof(int) + sizeof(char);

-       for (int i = 0; i < NUM_IPv6_TESTS; i++) {
+       for (int i = 0; i < NUM_IPv6_TESTS; i+=SUPPORTED_ALIGNMENT) {
                 saddr = (const struct in6_addr *)(random_buf + i);
                 daddr = (const struct in6_addr *)(random_buf + i +
                                                   daddr_offset);