diff mbox series

[17/17] x86/fpu: Move FPU initialization into arch_cpu_finalize_init()

Message ID 20230613224545.902376621@linutronix.de
State New
Headers
Series init, treewide, x86: Cleanup check_bugs() and start sanitizing the x86 boot process |

Commit Message

Thomas Gleixner June 13, 2023, 11:39 p.m. UTC 
  Initializing the FPU during the early boot process is a pointless
exercise. Early boot is convoluted and fragile enough.

Nothing requires that the FPU is set up early. It has to be initialized
before fork_init() because the task_struct size depends on the FPU register
buffer size.

Move the initialization to arch_cpu_finalize_init() which is the perfect
place to do so.

No functional change.

This allows to remove quite some of the custom early command line parsing,
but that's subject to the next installment.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/common.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Comments

Chang S. Bae June 14, 2023, 5:03 a.m. UTC | #1 
On 6/13/2023 4:39 PM, Thomas Gleixner wrote:
>   
> @@ -2396,6 +2393,13 @@ void __init arch_cpu_finalize_init(void)
>   			'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
>   	}
>   
> +	/*
> +	 * Must be before alternatives because it might set or clear
> +	 * feature bits.
> +	 */
> +	fpu__init_system();
> +	fpu__init_cpu();

fpu__init_cpu() appears to be duplicated here because fpu__init_system() 
invoked this already:

void __init fpu__init_system(void)
{
...
	/*
	 * The FPU has to be operational for some of the
	 * later FPU init activities:
	 */
	fpu__init_cpu();
...
}

https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/tree/arch/x86/kernel/fpu/init.c?h=init#n223

Thanks,
Chang
Thomas Gleixner June 14, 2023, 9:52 a.m. UTC | #2 
On Tue, Jun 13 2023 at 22:03, Chang S. Bae wrote:

> On 6/13/2023 4:39 PM, Thomas Gleixner wrote:
>>   
>> @@ -2396,6 +2393,13 @@ void __init arch_cpu_finalize_init(void)
>>   			'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
>>   	}
>>   
>> +	/*
>> +	 * Must be before alternatives because it might set or clear
>> +	 * feature bits.
>> +	 */
>> +	fpu__init_system();
>> +	fpu__init_cpu();
>
> fpu__init_cpu() appears to be duplicated here because fpu__init_system() 
> invoked this already:
>
> void __init fpu__init_system(void)
> {
> ...
> 	/*
> 	 * The FPU has to be operational for some of the
> 	 * later FPU init activities:
> 	 */
> 	fpu__init_cpu();

Well, that's _before_ xstate initialization and I couldn't convince
myself that it's good enough. All of this is such a horrible mess...
diff mbox series

Patch

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1604,8 +1604,6 @@  static void __init early_identify_cpu(st
 
 	sld_setup(c);
 
-	fpu__init_system();
-
 #ifdef CONFIG_X86_32
 	/*
 	 * Regardless of whether PCID is enumerated, the SDM says
@@ -2287,8 +2285,6 @@  void cpu_init(void)
 
 	doublefault_init_cpu_tss();
 
-	fpu__init_cpu();
-
 	if (is_uv_system())
 		uv_cpu_init();
 
@@ -2304,6 +2300,7 @@  void cpu_init_secondary(void)
 	 */
 	cpu_init_exception_handling();
 	cpu_init();
+	fpu__init_cpu();
 }
 #endif
 
@@ -2396,6 +2393,13 @@  void __init arch_cpu_finalize_init(void)
 			'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 	}
 
+	/*
+	 * Must be before alternatives because it might set or clear
+	 * feature bits.
+	 */
+	fpu__init_system();
+	fpu__init_cpu();
+
 	alternative_instructions();
 
 	if (IS_ENABLED(CONFIG_X86_64)) {