Re: [PATCH v12 2/7] arm64: cpufeature: add FEAT_LSUI

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Jan 21, 2026 at 07:06:17PM +0000, Yeoreum Yun wrote:
> +#ifdef CONFIG_ARM64_LSUI
> +static bool has_lsui(const struct arm64_cpu_capabilities *entry, int scope)
> +{
> +	if (!has_cpuid_feature(entry, scope))
> +		return false;
> +
> +	/*
> +	 * A CPU that supports LSUI should also support FEAT_PAN,
> +	 * so that SW_PAN handling is not required.
> +	 */
> +	if (WARN_ON(!__system_matches_cap(ARM64_HAS_PAN)))
> +		return false;
> +
> +	return true;
> +}
> +#endif

I still find this artificial dependency a bit strange. Maybe one doesn't
want any PAN at all (software or hardware) and won't get LSUI either
(it's unlikely but possible).

We have the uaccess_ttbr0_*() calls already for !LSUI, so maybe
structuring the macros in a way that they also take effect with LSUI.
For futex, we could add some new functions like uaccess_enable_futex()
which wouldn't do anything if LSUI is enabled with hw PAN.

-- 
Catalin