linux-kernel - Re: [PATCH v2 13/20] x86/asm/64: Pass sp0 directly to load

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Date:   Thu, 2 Nov 2017 10:48:13 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 13/20] x86/asm/64: Pass sp0 directly to load_sp0()


* Andy Lutomirski <luto@...nel.org> wrote:

> load_sp0() had an odd signature:
> 
> void load_sp0(struct tss_struct *tss, struct thread_struct *thread);
> 
> Simplify it to:
> 
> void load_sp0(unsigned long sp0);

I also added this to the changelog:

> Also simplify a few get_cpu()/put_cpu() sequences to
> preempt_disable()/preempt_enable().

Plus:

> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1572,7 +1572,7 @@ void cpu_init(void)
>  	initialize_tlbstate_and_flush();
>  	enter_lazy_tlb(&init_mm, me);
>  
> -	load_sp0(t, &current->thread);
> +	load_sp0(current->thread.sp0);
>  	set_tss_desc(cpu, t);
>  	load_TR_desc();
>  	load_mm_ldt(&init_mm);
> @@ -1627,7 +1627,7 @@ void cpu_init(void)
>  	initialize_tlbstate_and_flush();
>  	enter_lazy_tlb(&init_mm, curr);
>  
> -	load_sp0(t, thread);
> +	load_sp0(thread->sp0);
>  	set_tss_desc(cpu, t);
>  	load_TR_desc();
>  	load_mm_ldt(&init_mm);

In the 32-bit path this was the last use of 'thread', making the local variable 
unused - I removed it.

Just curious: did you build/boot-test 32-bit kernels, or should we consider it 
mostly untested?

Thanks,

	Ingo