linux-kernel - Re: [PATCH] x86/trampoline: fallback to fixed trampoline address if no e820 map is provided

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Date:	Thu, 23 Dec 2010 10:57:34 +0100
From:	Florian Fainelli <ffainelli@...ebox.fr>
To:	linux-kernel@...r.kernel.org
Cc:	Dirk Brandewie <dirk.brandewie@...il.com>, sodaville@...utronix.de,
	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH] x86/trampoline: fallback to fixed trampoline address if no e820 map is provided

On Tuesday 14 December 2010 22:19:39 Florian Fainelli wrote:
> From: Florian Fainelli <ffainelli@...ebox.fr>
> 
> Since 893f38d1 (x86: Use find_e820() instead of hard coded trampoline
> address), the trampoline base address should be provided by the BIOS as an
> e820 area. Some minimalistic BIOSes (like CEFDK on CE4100) may not provide
> any e820 area, still we should fallback to a fixed trampoline base address
> for SMP to work correctly.
> 
> Cc: Dirk Brandewie <dirk.brandewie@...il.com>
> Cc: sodaville@...utronix.de
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Florian Fainelli <ffainelli@...ebox.fr>

Ingo, Yinghai, anything wrong with that patch? Thank you.

> ---
> diff --git a/arch/x86/include/asm/trampoline.h
> b/arch/x86/include/asm/trampoline.h index f4500fb..908b395 100644
> --- a/arch/x86/include/asm/trampoline.h
> +++ b/arch/x86/include/asm/trampoline.h
> @@ -16,6 +16,7 @@ extern unsigned long initial_code;
>  extern unsigned long initial_gs;
> 
>  #define TRAMPOLINE_SIZE roundup(trampoline_end - trampoline_data,
> PAGE_SIZE) +#define TRAMPOLINE_BASE 0x6000
> 
>  extern unsigned long setup_trampoline(void);
>  extern void __init reserve_trampoline_memory(void);
> diff --git a/arch/x86/kernel/trampoline.c b/arch/x86/kernel/trampoline.c
> index f1488a3..d025aae 100644
> --- a/arch/x86/kernel/trampoline.c
> +++ b/arch/x86/kernel/trampoline.c
> @@ -21,8 +21,11 @@ void __init reserve_trampoline_memory(void)
> 
>  	/* Has to be in very low memory so we can execute real-mode AP code. */
>  	mem = find_e820_area(0, 1<<20, TRAMPOLINE_SIZE, PAGE_SIZE);
> -	if (mem == -1L)
> -		panic("Cannot allocate trampoline\n");
> +	if (mem == -1L) {
> +		printk(KERN_INFO "BIOS did not provide e820 area for trampoline"
> +				" ,using static trampoline address\n");
> +		mem = TRAMPOLINE_BASE;
> +	}
> 
>  	trampoline_base = __va(mem);
>  	reserve_early(mem, mem + TRAMPOLINE_SIZE, "TRAMPOLINE");
--
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