Re: [PATCH v2 1/2] x86/cpu: Disable CR pinning during CPU bringup

[Chang S. Bae]

On 3/13/2026 1:35 AM, Nikunj A. Dadhania wrote:
>   
> +	/*
> +	 * CPUs that support FSGSBASE may use RDGSBASE/WRGSBASE in
> +	 * paranoid_entry(). Enable the feature before any exceptions
> +	 * occur.
> +	 */

To ensure this not bite back again, maybe better to document the detail 
on the way the entry code was shaped out here (or somewhere else):

  To APs, the exception entry code was already patched when available,
  which means those instructions will execute unconditionally there. So,
  APs must set CR4.FSGSBASE as early as possible.

> +	if (cpu_feature_enabled(X86_FEATURE_FSGSBASE)) {
> +		cr4_set_bits(X86_CR4_FSGSBASE);
> +		elf_hwcap2 |= HWCAP2_FSGSBASE;
> +	}
> +