Re: [PATCH v2 3/3] powerpc/mm: Implement CONFIG_DEBUG_RODATA on PPC32

[Naveen N. Rao]

Excerpts from Christophe Leroy's message of April 21, 2017 18:32:

This patch implements CONFIG_DEBUG_RODATA on PPC32.

As for CONFIG_DEBUG_PAGEALLOC, it deactivates BAT and LTLB mappings
in order to allow page protection setup at the level of each page.

As BAT/LTLB mappings are deactivated, their might be performance
impact. For this reason, we keep it OFF by default.

Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>

[snip]

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c

index 32509de6ce4c..06d2ac53f471 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -46,6 +46,7 @@ static int
 ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
 {
        unsigned int replaced;
+       int err;

        /*
         * Note:
@@ -67,10 +68,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, 
unsigned int new)
        }

        /* replace the text with the new text */
-       if (patch_instruction((unsigned int *)ip, new))
-               return -EPERM;
+       set_kernel_text_rw(ip);
+       err = patch_instruction((unsigned int *)ip, new);
+       set_kernel_text_ro(ip);

Is there a reason to not put those inside patch_instruction()?

- Naveen