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

[Sohil Mehta <sohil.mehta@intel.com>]

On 3/13/2026 1:35 AM, Nikunj A. Dadhania wrote:
> @@ -2413,6 +2407,16 @@ void cpu_init_exception_handling(bool boot_cpu)
>  	/* GHCB needs to be setup to handle #VC. */
>  	setup_ghcb();
>  
> +	/*
> +	 * CPUs that support FSGSBASE may use RDGSBASE/WRGSBASE in
> +	 * paranoid_entry(). Enable the feature before any exceptions
> +	 * occur.
> +	 */
> +	if (cpu_feature_enabled(X86_FEATURE_FSGSBASE)) {
> +		cr4_set_bits(X86_CR4_FSGSBASE);
> +		elf_hwcap2 |= HWCAP2_FSGSBASE;
> +	}
> +

There is already a lot happening in this function. If we end up going
this route, I would suggest moving this to a small wrapper function such
as setup_fsgsbase() or enable_fsgsbase().

cpu_init_exception_handling() doesn't seem to be in a hot-path and
cpu_feature_enabled(X86_FEATURE_FSGSBASE) is generally expected to be
true on modern CPUs.


>  	if (cpu_feature_enabled(X86_FEATURE_FRED)) {
>  		/* The boot CPU has enabled FRED during early boot */
>  		if (!boot_cpu)
> 
> Regards,
> Nikunj
> 
>