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Date:   Fri, 17 Apr 2020 17:22:47 -0700 (PDT)
Subject:     Re: [PATCH v5 3/9] riscv: patch code by fixmap mapping
In-Reply-To: <27f31750f58cd0ad2805579b16b001aa88103688.1586332296.git.zong.li@sifive.com>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        mhiramat@kernel.org, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, zong.li@sifive.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     zong.li@sifive.com
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On Wed, 08 Apr 2020 00:56:58 PDT (-0700), zong.li@sifive.com wrote:
> On strict kernel memory permission, the ftrace have to change the
> permission of text for dynamic patching the intructions. Use
> riscv_patch_text_nosync() to patch code instead of probe_kernel_write.
>
> Signed-off-by: Zong Li <zong.li@sifive.com>
> Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  arch/riscv/kernel/ftrace.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index c40fdcdeb950..08396614d6f4 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -7,9 +7,23 @@
>
>  #include <linux/ftrace.h>
>  #include <linux/uaccess.h>
> +#include <linux/memory.h>
>  #include <asm/cacheflush.h>
> +#include <asm/patch.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> +{
> +	mutex_lock(&text_mutex);
> +	return 0;
> +}
> +
> +int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> +{
> +	mutex_unlock(&text_mutex);
> +	return 0;
> +}
> +
>  static int ftrace_check_current_call(unsigned long hook_pos,
>  				     unsigned int *expected)
>  {
> @@ -46,20 +60,14 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
>  {
>  	unsigned int call[2];
>  	unsigned int nops[2] = {NOP4, NOP4};
> -	int ret = 0;
>
>  	make_call(hook_pos, target, call);
>
> -	/* replace the auipc-jalr pair at once */
> -	ret = probe_kernel_write((void *)hook_pos, enable ? call : nops,
> -				 MCOUNT_INSN_SIZE);
> -	/* return must be -EPERM on write error */
> -	if (ret)
> +	/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
> +	if (patch_text_nosync
> +	    ((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))
>  		return -EPERM;
>
> -	smp_mb();
> -	flush_icache_range((void *)hook_pos, (void *)hook_pos + MCOUNT_INSN_SIZE);
> -
>  	return 0;
>  }

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>