linux-kernel - Re: [PATCH] [GIT PULL] tracing: allow to change permissions for text with dynamic ftrace enabled

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Date:	Tue, 27 Oct 2009 19:11:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] [GIT PULL] tracing: allow to change permissions for
	text with dynamic ftrace enabled


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

> 
> Ingo,
> 
> The cause of the ftrace bug you saw in tip/master was caused by a change
> in tip's x86/mm branch.
> 
> Please pull the latest tip/x86/mm tree, which can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> tip/x86/mm
> 
> 
> Steven Rostedt (1):
>       tracing: allow to change permissions for text with dynamic ftrace enabled
> 
> ----
>  arch/x86/mm/pageattr.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> ---------------------------
> commit 883242dd0e5faaba041528a9a99f483f2a656c83
> Author: Steven Rostedt <srostedt@...hat.com>
> Date:   Tue Oct 27 13:15:11 2009 -0400
> 
>     tracing: allow to change permissions for text with dynamic ftrace enabled
>     
>     The commit 74e081797bd9d2a7d8005fe519e719df343a2ba8
>     x86-64: align RODATA kernel section to 2MB with CONFIG_DEBUG_RODATA
>     prevents text sections from becoming read/write using set_memory_rw.
>     
>     The dynamic ftrace changes all text pages to read/write just before
>     converting the calls to tracing to nops, and vice versa.
>     
>     I orginally just added a flag to allow this transaction when ftrace
>     did the change, but I also found that when the CPA testing was running
>     it would remove the read/write as well, and ftrace does not do the text
>     conversion on boot up, and the CPA changes caused the dynamic tracer
>     to fail on self tests.
>     
>     The current solution I have is to simply not to prevent
>     change_page_attr from setting the RW bit for kernel text pages.
>     
>     Reported-by: Ingo Molnar <mingo@...e.hu>
>     Cc: Suresh Siddha <suresh.b.siddha@...el.com>
>     Cc: H. Peter Anvin <hpa@...or.com>
>     Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index b494fc4..78d3168 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -279,7 +279,8 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
>  		   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
>  		pgprot_val(forbidden) |= _PAGE_RW;
>  
> -#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
> +#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) && \
> +	!defined(CONFIG_DYNAMIC_FTRACE)
>  	/*
>  	 * Kernel text mappings for the large page aligned .rodata section
>  	 * will be read-only. For the kernel identity mappings covering

Pulled, thanks Steve!

	Ingo
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