Re: [PATCH 0/2] x86/fred: enable FRED by default

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

On 3/23/2026 1:15 PM, H. Peter Anvin wrote:

Can we please include this as well?

diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
index e736b19e18de..117aa06d25ca 100644
--- a/arch/x86/kernel/fred.c
+++ b/arch/x86/kernel/fred.c
@@ -27,9 +27,6 @@ EXPORT_PER_CPU_SYMBOL(fred_rsp0);

 void cpu_init_fred_exceptions(void)
 {
-	/* When FRED is enabled by default, remove this log message */
-	pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
-
 	/*
 	 * If a kernel event is delivered before a CPU goes to user level for
 	 * the first time, its SS is NULL thus NULL is pushed into the SS field


> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 03a550630644..bfa8a20ccc37 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1750,8 +1750,8 @@ Kernel parameters
>  	fred=		[X86-64]
>  			Enable/disable Flexible Return and Event Delivery.
>  			Format: { on | off }
> -			on: enable FRED when it's present.
> -			off: disable FRED, the default setting.
> +			on: enable FRED when it's present, the default setting.

Why do we need the fred=on line after this series? It can't really
enable FRED when the compile option is disabled. Seems like a dead (and
slightly confusing) option to me.

> +			off: disable FRED.
>  
>  	ftrace=[tracer]
>  			[FTRACE] will set and start the specified tracer
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index e2df1b147184..876b663dcf38 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -557,7 +557,7 @@ config X86_FRED
>  	bool "Flexible Return and Event Delivery"
>  	depends on X86_64
>  	help
> -	  When enabled, try to use Flexible Return and Event Delivery
> +	  When enabled, use Flexible Return and Event Delivery
>  	  instead of the legacy SYSCALL/SYSENTER/IDT architecture for
>  	  ring transitions and exception/interrupt handling if the
>  	  system supports it.
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index a8ff4376c286..e22a49869380 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1746,7 +1746,7 @@ static void __init cpu_parse_early_param(void)
>  
>  	/* Minimize the gap between FRED is available and available but disabled. */
>  	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
> -	if (arglen != 2 || strncmp(arg, "on", 2))
> +	if (arglen > 0 && (arglen != 2 || strncmp(arg, "on", 2)))
>  		setup_clear_cpu_cap(X86_FEATURE_FRED);

Nit: Would it be better to compare with "off" rather than not on?

>  
>  	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));