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SubjectRe: [PATCH v2] powerpc: fix boot on BOOK3S_32 with CONFIG_STRICT_KERNEL_RWX
On Wed, Nov 22, 2017 at 1:28 AM, Christophe Leroy
<christophe.leroy@c-s.fr> wrote:
> On powerpc32, patch_instruction() is called by apply_feature_fixups()
> which is called from early_init()
>
> There is the following note in front of early_init():
> * Note that the kernel may be running at an address which is different
> * from the address that it was linked at, so we must use RELOC/PTRRELOC
> * to access static data (including strings). -- paulus
>
> Therefore, slab_is_available() cannot be called yet, and
> text_poke_area must be addressed with PTRRELOC()
>
> Fixes: 37bc3e5fd764f ("powerpc/lib/code-patching: Use alternate map
> for patch_instruction()")
> Reported-by: Meelis Roos <mroos@linux.ee>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> v2: Added missing asm/setup.h
>
> arch/powerpc/lib/code-patching.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index c9de03e0c1f1..d469224c4ada 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -21,6 +21,7 @@
> #include <asm/tlbflush.h>
> #include <asm/page.h>
> #include <asm/code-patching.h>
> +#include <asm/setup.h>
>
> static int __patch_instruction(unsigned int *addr, unsigned int instr)
> {
> @@ -146,11 +147,8 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
> * During early early boot patch_instruction is called
> * when text_poke_area is not ready, but we still need
> * to allow patching. We just do the plain old patching
> - * We use slab_is_available and per cpu read * via this_cpu_read
> - * of text_poke_area. Per-CPU areas might not be up early
> - * this can create problems with just using this_cpu_read()
> */
> - if (!slab_is_available() || !this_cpu_read(text_poke_area))
> + if (!this_cpu_read(*PTRRELOC(&text_poke_area)))
> return __patch_instruction(addr, instr);

On ppc64, we call apply_feature_fixups() in early_setup() after we've
relocated ourselves. Sorry for missing the ppc32 case. I would like to
avoid PTRRELOC when unnecessary.

Balbir Singh.

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