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

Naveen N. Rao
2017-04-21T13:33:52Z

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.leroy@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