linux-kernel - Re: [PATCH 1/1] headers/deps: x86/fpu: Make task

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Date: Tue, 26 Mar 2024 18:49:03 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave@...1.net>, Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, "H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH 1/1] headers/deps: x86/fpu: Make task_struct::thread
 constant size

On 03/20, Ingo Molnar wrote:
>
> --- a/arch/x86/kernel/fpu/init.c
> +++ b/arch/x86/kernel/fpu/init.c
> @@ -38,7 +38,7 @@ static void fpu__init_cpu_generic(void)
>  	/* Flush out any pending x87 state: */
>  #ifdef CONFIG_MATH_EMULATION
>  	if (!boot_cpu_has(X86_FEATURE_FPU))
> -		fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
> +		fpstate_init_soft(current->thread.fpu->fpstate->regs.soft);
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Typo? it should be

	&current->thread.fpu->fpstate->regs.soft

> +static struct fpu x86_init_fpu __read_mostly;
> +
>  static void __init fpu__init_system_early_generic(void)
>  {
> +	{
> +		int this_cpu = smp_processor_id();
> +
> +		fpstate_reset(&x86_init_fpu);
> +		current->thread.fpu = &x86_init_fpu;
> +		per_cpu(fpu_fpregs_owner_ctx, this_cpu) = &x86_init_fpu;
> +		x86_init_fpu.last_cpu = this_cpu;
> +	}

Can't x86_init_fpu be declared inside the block above?

>  void __init fpu__init_system(void)
>  {
> -	fpstate_reset(&current->thread.fpu);
>  	fpu__init_system_early_generic();
> +	fpstate_reset(current->thread.fpu);

It seems that fpstate_reset(current->thread.fpu) is not needed after the
change in fpu__init_system_early_generic() above.

Oleg.