linux-kernel - Re: [PATCH 16/21] x86/entry/64: Use a per-CPU trampoline stack for IDT entries

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Date:   Fri, 1 Dec 2017 09:06:32 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 16/21] x86/entry/64: Use a per-CPU trampoline stack for
 IDT entries

On 11/27/2017 02:45 AM, Ingo Molnar wrote:
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1645,11 +1645,13 @@ void cpu_init(void)
>  	setup_cpu_entry_area(cpu);
>  
>  	/*
> -	 * Initialize the TSS.  Don't bother initializing sp0, as the initial
> -	 * task never enters user mode.
> +	 * Initialize the TSS.  sp0 points to the entry trampoline stack
> +	 * regardless of what task is running.
>  	 */
>  	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
>  	load_TR_desc();
> +	load_sp0((unsigned long)&get_cpu_entry_area(cpu)->tss +
> +		 offsetofend(struct tss_struct, SYSENTER_stack));
>  
>  	load_mm_ldt(&init_mm);

Does this also mean that our stack dumps will say "<SYSENTER>" in oopses?

> [   30.811750] CR2: fffffffffdeb2f98 CR3: 0000000423fae001 CR4: 00000000001607e0                                                                                                           
> [   30.819712] Call Trace:                                                                                                                                                                 
> [   30.822442]  <SYSENTER>                                                                                                                                                                 
> [   30.825170]  trace_hardirqs_on_thunk+0x1c/0x1c                                                                                                                                          
...
> [   31.000571] R13: 0000000000000050 R14: 0000000000000076 R15: 00007f59f76f2d60                                                                                                           
> [   31.008533]  </SYSENTER>                                                                                                    

Should we change that string to something more descriptive?