linux-kernel - Re: [PATCH] selftests/mm: Skip test for non-LPA2 and non-LVA systems

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Message-ID: <3782befb-c317-4bb0-a279-c90adb2ec47b@arm.com>
Date: Wed, 17 Jul 2024 17:41:27 +0530
From: Dev Jain <dev.jain@....com>
To: Ryan Roberts <ryan.roberts@....com>, akpm@...ux-foundation.org,
 shuah@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-mm@...ck.org, Anshuman.Khandual@....com, broonie@...nel.org
Subject: Re: [PATCH] selftests/mm: Skip test for non-LPA2 and non-LVA systems


On 7/17/24 17:27, Ryan Roberts wrote:
> On 17/07/2024 12:10, Dev Jain wrote:
>> Post my improvement of the test:
>> https://lore.kernel.org/all/20240522070435.773918-3-dev.jain@arm.com/
>> The test begins to fail on 4k and 16k pages, on non-LPA2 systems. To
>> reduce noise in the CI systems, let us skip the test when higher address
>> space is not implemented.
>>
>> Signed-off-by: Dev Jain <dev.jain@....com>
>> ---
>> The patch applies on linux-next.
>>
>>   tools/testing/selftests/mm/va_high_addr_switch.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/va_high_addr_switch.c b/tools/testing/selftests/mm/va_high_addr_switch.c
>> index fa7eabfaf841..c6040e1d6e53 100644
>> --- a/tools/testing/selftests/mm/va_high_addr_switch.c
>> +++ b/tools/testing/selftests/mm/va_high_addr_switch.c
>> @@ -293,6 +293,18 @@ static int run_test(struct testcase *test, int count)
>>   	return ret;
>>   }
>>   
>> +/* Check if userspace VA > 48 bits */
>> +static int high_address_present(void)
>> +{
>> +	void *ptr = mmap((void *)(1UL << 50), 1, PROT_READ | PROT_WRITE,
>> +			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
> I think there is (very unlikely) possibility that something is already mapped at
> this address so it will be replaced due to MAP_FIXED. That could break the test.
> But the only way something could be already mapped is if ARM64_FORCE_52BIT is
> set and in that case, the test will fail anyway, right? So I think this is fine.

The testcases already assume that high addresses must be empty. Yes, FORCE_52BIT
is the only way something could already be mapped at high addresses, but in that
case the test fails trivially.

>
>> +	if (ptr == MAP_FAILED)
>> +		return 0;
>> +
>> +	munmap(ptr, 1);
>> +	return 1;
>> +}
> I'm guessing this will cause a function-not-used warning on arches other than
> arm64? Perhaps wrap it in `#ifdef __aarch64__`?

Ah yes, I just checked and that is true. I shall post v2 in some time, shall
wait if any more comments are there.

>
> Thanks,
> Ryan
>
>> +
>>   static int supported_arch(void)
>>   {
>>   #if defined(__powerpc64__)
>> @@ -300,7 +312,7 @@ static int supported_arch(void)
>>   #elif defined(__x86_64__)
>>   	return 1;
>>   #elif defined(__aarch64__)
>> -	return 1;
>> +	return high_address_present();
>>   #else
>>   	return 0;
>>   #endif