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

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Message-ID: <423341da-57ae-4e44-a7f6-74f8ebfd3962@arm.com>
Date: Wed, 17 Jul 2024 13:25:01 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Dev Jain <dev.jain@....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 17/07/2024 13:11, Dev Jain wrote:
> 
> 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.

agreed.

> 
>>
>>> +    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.

With this fixup:

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> 
>>
>> 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