Re: [PATCH] selftests/proc: proc-empty-vm: handle CPUs without protection keys

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 09/11/2026 16:19, Kurt Lin wrote:
> On x86 CPUs without protection keys, pkey_alloc() fails with ENOSPC,
> as documented in pkey_alloc(2). protection_key_support() only expects
> ENOSYS or EINVAL, so the test fails on such machines, e.g. an Intel
> Core i5-7200U:

It would be good to mention that the x86 implementation had a bug where
the first call to pkey_alloc() would return -EINVAL instead of -ENOSPC.
This was recently fixed by commit dee87e09b0dd ("x86/pkeys: Fix
pkey_alloc() return value when pkeys are not supported"); that's
probably why the issue appeared only now.

-EINVAL is technically not an expected error in this situation, but for
backwards-compatibility with older kernels it probably makes sense to
allow it for a little while.

With the commit message expanded:

Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>

>   protection_key_support: error: rv -1, errno 28
>
> Treat ENOSPC as "no protection key support" as well.
>
> An AI coding assistant (Claude) was used to analyze the failure and to
> draft the fix and this changelog. Tested on v7.4-rc1 on the machine
> above; the test now passes.
>
> Fixes: bf5add391eeb ("proc: test ProtectionKey in proc-empty-vm test")
> Signed-off-by: Kurt Lin <lylin1023@gmail.com>
> ---
>  tools/testing/selftests/proc/proc-empty-vm.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/testing/selftests/proc/proc-empty-vm.c b/tools/testing/selftests/proc/proc-empty-vm.c
> index b3f898aab4ab..a9d3c973a663 100644
> --- a/tools/testing/selftests/proc/proc-empty-vm.c
> +++ b/tools/testing/selftests/proc/proc-empty-vm.c
> @@ -77,6 +77,9 @@ static int protection_key_support(void)
>  	} else if (rv == -1 && errno == EINVAL) {
>  		// ospke=n
>  		return 0;
> +	} else if (rv == -1 && errno == ENOSPC) {
> +		// CPU without protection keys
> +		return 0;
>  	} else {
>  		fprintf(stderr, "%s: error: rv %ld, errno %d\n", __func__, rv, errno);
>  		exit(EXIT_FAILURE);