Le 19/04/2017 à 16:22, Christophe LEROY a écrit :

Le 19/04/2017 à 16:01, Michael Ellerman a écrit :

quoted

Christophe Leroy [off-list ref] writes:

quoted

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 32509de6ce4c..4af81fb23653 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c

@@ -526,7 +526,9 @@ void ftrace_replace_code(int enable)
  */
 void arch_ftrace_update_code(int command)
 {
+    set_kernel_text_rw();
     ftrace_modify_all_code(command);
+    set_kernel_text_ro();
 }

I'm not sure that's the right place for that.

I took arch/arm/ as model. It does the following. Is that wrong ?


static int __ftrace_modify_code(void *data)
{
    int *command = data;

    set_kernel_text_rw();
    ftrace_modify_all_code(*command);
    set_kernel_text_ro();

    return 0;
}

void arch_ftrace_update_code(int command)
{
    stop_machine(__ftrace_modify_code, &command, NULL);
}

quoted

If you look at other arches they hook into ftrace_modify_code(), where
you have the address that's being modified.

Ok, I will look at other arches.

Could you provide more details on what you have seen on other arches ? I 
didn't notice anything related in any other arches' ftrace_modify_code()

What I could find however is, in x86, the use of 
ftrace_arch_code_modify_prepare() and 
ftrace_arch_code_modify_post_process ():

int ftrace_arch_code_modify_prepare(void)
{
	set_kernel_text_rw();
	set_all_modules_text_rw();
	return 0;
}

int ftrace_arch_code_modify_post_process(void)
{
	set_all_modules_text_ro();
	set_kernel_text_ro();
	return 0;
}


Those functions are also used on arm but only for modules:

int ftrace_arch_code_modify_prepare(void)
{
	set_all_modules_text_rw();
	return 0;
}

int ftrace_arch_code_modify_post_process(void)
{
	set_all_modules_text_ro();
	/* Make sure any TLB misses during machine stop are cleared. */
	flush_tlb_all();
	return 0;
}


Should I apply the x86 approach, or something else ?

Christophe

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