linux-kernel - Re: [PATCH] x86, traps: early_trap

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Date:	Fri, 27 Feb 2015 11:11:59 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	luto@...capital.net, lizefan@...wei.com, mingo@...nel.org,
	masami.hiramatsu.pt@...achi.com, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, linux-tip-commits@...r.kernel.org,
	tglx@...utronix.de, hpa@...or.com, dave.hansen@...ux.intel.com,
	oleg@...hat.com
Subject: Re: [PATCH] x86, traps: early_trap_init() cleanup.

On Fri, Feb 27, 2015 at 11:28:50AM +0800, Wang Nan wrote:
> As early_trap_init() doesn't use IST, replace set_intr_gate_ist(..., 0)
> and set_system_intr_gate_ist(..., 0) with their standard counterparts.
> 
> set_intr_gate() requires a trace_debug symbol which we don't have and
> won't use. Use a small macro trick as a workaround.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
> 
> Hi Andy Lutomirski,
> 
>    This patch is a bit tricky, but I think we don't need to define another
>    helper for such a small problem. What's your opinion?
> 
> Thank you!
> 
> ---
>  arch/x86/kernel/traps.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 4281988..c24434a 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -925,17 +925,22 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
>  /* Set of traps needed for early debugging. */
>  void __init early_trap_init(void)
>  {
> +
>  	/*
> -	 * Don't set ist to DEBUG_STACK as it doesn't work until TSS is
> -	 * ready in cpu_init() <-- trap_init(). Before trap_init(), CPU
> -	 * runs at ring 0 so it is impossible to hit an invalid stack.
> -	 * Using the original stack works well enough at this early
> -	 * stage. DEBUG_STACK will be equipped after cpu_init() in
> -	 * trap_init().
> +	 * Don't use IST to set DEBUG_STACK as it doesn't work until TSS is
> +	 * ready in cpu_init() <-- trap_init(). Before trap_init(), CPU runs at
> +	 * ring 0 so it is impossible to hit an invalid stack.  Using the
> +	 * original stack works well enough at this early stage. DEBUG_STACK
> +	 * will be equipped after cpu_init() in trap_init().
> +	 *
> +	 * Since set_intr_gate() needs a trace_debug but we don't have it,
> +	 * use the following #define as a workaround.
>  	 */
> -	set_intr_gate_ist(X86_TRAP_DB, &debug, 0);
> +#define trace_debug debug

This goes to arch/x86/include/asm/traps.h like the rest of the trace_*
defines.

> +	set_intr_gate(X86_TRAP_DB, debug);
> +#undef trace_debug
>  	/* int3 can be called from all */
> -	set_system_intr_gate_ist(X86_TRAP_BP, &int3, 0);
> +	set_system_intr_gate(X86_TRAP_BP, &int3);
>  #ifdef CONFIG_X86_32
>  	set_intr_gate(X86_TRAP_PF, page_fault);
>  #endif

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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