Re: [PATCH -v5 13/17] arm/ftrace: Use __patch_text_real()

Will Deacon
2019-11-11T16:47:13Z

On Mon, Nov 11, 2019 at 02:13:05PM +0100, Peter Zijlstra wrote:
> Instead of flipping text protection, use the patch_text infrastructure
> that uses a fixmap alias where required.
>
> This removes the last user of set_all_modules_text_*().
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: ard.biesheuvel@linaro.org
> Cc: rabin@rab.in
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: james.morse@arm.com
> ---
> arch/arm/kernel/ftrace.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -22,6 +22,7 @@
> #include <asm/ftrace.h>
> #include <asm/insn.h>
> #include <asm/set_memory.h>
> +#include <asm/patch.h>
>
> #ifdef CONFIG_THUMB2_KERNEL
> #define NOP 0xf85deb04 /* pop.w {lr} */
> @@ -31,13 +32,15 @@
>
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> +static int patch_text_remap = 0;
> +
> static int __ftrace_modify_code(void *data)
> {
> int *command = data;
>
> - set_kernel_text_rw();
> + patch_text_remap++;
> ftrace_modify_all_code(*command);
> - set_kernel_text_ro();
> + patch_text_remap--;
>
> return 0;
> }
> @@ -59,13 +62,13 @@ static unsigned long adjust_address(stru
>
> int ftrace_arch_code_modify_prepare(void)
> {
> - set_all_modules_text_rw();
> + patch_text_remap++;
> return 0;
> }
>
> int ftrace_arch_code_modify_post_process(void)
> {
> - set_all_modules_text_ro();
> + patch_text_remap--;
> /* Make sure any TLB misses during machine stop are cleared. */
> flush_tlb_all();
> return 0;
> @@ -97,10 +100,7 @@ static int ftrace_modify_code(unsigned l
> return -EINVAL;
> }
>
> - if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
> - return -EPERM;
> -
> - flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
> + __patch_text_real((void *)pc, new, patch_text_remap);

I'd still prefer to pass 'true' unconditionally here, since I don't think
this is a hot path.

Will