linux-kernel - Re: [PATCH 2/5] ftrace, x86: make kernel text writable only for conversions

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Message-ID: <20090220173035.GI24538@elte.hu>
Date:	Fri, 20 Feb 2009 18:30:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/5] ftrace, x86: make kernel text writable only for
	conversions


* Steven Rostedt <rostedt@...dmis.org> wrote:

> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index b55b4a7..5564cf3 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -80,4 +80,14 @@ extern void return_to_handler(void);
>  #endif /* __ASSEMBLY__ */
>  #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>  
> +#ifndef __ASSEMBLY__
> +#ifdef CONFIG_DEBUG_RODATA
> +void set_kernel_text_rw(void);
> +void set_kernel_text_ro(void);
> +#else
> +static inline void set_kernel_text_rw(void) { }
> +static inline void set_kernel_text_ro(void) { }
> +#endif
> +#endif /* __ASSEMBLY__ */

The proper place for this is where the other pagetable attribute 
functions reside: arch/x86/include/asm/cacheflush.h.

> +/* used by ftrace */
> +void set_kernel_text_rw(void)
> +{
> +	unsigned long start = PFN_ALIGN(_text);
> +	unsigned long size = PFN_ALIGN(_etext) - start;
> +
> +	printk(KERN_INFO "Set kernel text: %lx - %lx for read write\n",
> +	       start, start+size);
> +
> +	set_pages_rw(virt_to_page(start), size >> PAGE_SHIFT);

Wont this be executed by every suspend/resume cycle? I'm not 
sure we want a KERN_INFO printout every time.

> +/* used by ftrace */
> +void set_kernel_text_rw(void)

i'd leave out the 'used by ftrace' bit - more uses might arise. 
How does kprobes get around readonly pages, it uses these APIs 
too, right?

	Ingo
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