Re: [PATCH v5 01/13] arm64: cpufeature: __this_cpu_has_cap() shouldn't stop early

Suzuki K Poulose
2017-12-15T16:20:41Z

On 15/12/17 15:50, James Morse wrote:
> this_cpu_has_cap() tests caps->desc not caps->matches, so it stops
> walking the list when it finds a 'silent' feature, instead of
> walking to the end of the list.
>
> Prior to v4.6's 644c2ae198412 ("arm64: cpufeature: Test 'matches' pointer
> to find the end of the list") we always tested desc to find the end of
> a capability list. This was changed for dubious things like PAN_NOT_UAO.
> v4.7's e3661b128e53e ("arm64: Allow a capability to be checked on
> single CPU") added this_cpu_has_cap() using the old desc style test.
>
> CC: Suzuki K Poulose <suzuki.poulose@arm.com>
> CC: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> So far only ARM64_HAS_SYSREG_GIC_CPUIF and errata use this_cpu_has_cap(),
> all the errata have descriptions, and the GIC_CPUIF feature is first in
> the list, so its not possible to hit this with mainline. I don't think
> this should go to stable - this is not intended as a fix.
>
> arch/arm64/kernel/cpufeature.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index c5ba0097887f..68a49f7fb75c 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1236,8 +1236,8 @@ static bool __this_cpu_has_cap(const struct arm64_cpu_capabilities *cap_array,
> if (WARN_ON(preemptible()))
> return false;
>
> - for (caps = cap_array; caps->desc; caps++)
> - if (caps->capability == cap && caps->matches)
> + for (caps = cap_array; caps->matches; caps++)
> + if (caps->capability == cap)
> return caps->matches(caps, SCOPE_LOCAL_CPU);

Thanks for catching this !

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>