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

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Message-ID: <da0054f5-b84e-4635-ae81-9c72f2f25542@arm.com>
Date: Wed, 17 Jul 2024 12:57:00 +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 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.

> +	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__`?

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