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Subject: Re: [PATCH v3 2/4] selftests/arm64: Treat KSM merge_across_nodes as
 optional
To: Muhammad Usama Anjum <usama.anjum@arm.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Mark Rutland <mark.rutland@arm.com>, Shuah Khan <shuah@kernel.org>,
 Andrey Konovalov <andreyknvl@gmail.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 Amit Daniel Kachhap <amit.kachhap@arm.com>, Yeoreum Yun
 <yeoreum.yun@arm.com>, Mark Brown <broonie@kernel.org>,
 open list <linux-kernel@vger.kernel.org>,
 "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
 <linux-arm-kernel@lists.infradead.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>
References: <20260825111929.2882324-1-usama.anjum@arm.com>
 <20260825111929.2882324-3-usama.anjum@arm.com>
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From: Vincenzo Frascino <vincenzo.frascino@arm.com>
In-Reply-To: <20260825111929.2882324-3-usama.anjum@arm.com>
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On 25/08/2026 12:18, Muhammad Usama Anjum wrote:
> The MTE KSM test requires write access to KSM sysfs but does not check
> that it is running as root. It also unconditionally saves, enables and
> restores the merge_across_nodes attribute. The kernel only creates this
> attribute when CONFIG_NUMA=y, so a non-NUMA kernel prints the following
> message three times even though every KSM subtest passes:
> 
>   # ERR: missing /sys/kernel/mm/ksm/merge_across_nodes
> 
> Skip the test when it is not running as root. Check that the optional
> attribute is readable and writable, treating ENOENT as its expected
> absence on non-NUMA kernels and skipping the test for other access
> failures. Only save, enable and restore the attribute when it is
> available.
> 
> Check MTE availability before the privilege and sysfs checks so systems
> without MTE retain the existing feature-unavailable skip result.
> 
> This preserves the existing behavior on NUMA kernels without requiring
> NUMA or reducing KSM coverage on single-node systems.
> 
> Fixes: f981d8fa2646 ("kselftest/arm64: Verify KSM page merge for MTE pages")
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

...