linux-kernel - Re: [PATCH 4/7] riscv: Simplify text patching loops

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Message-ID: <874je4fvxl.fsf@all.your.base.are.belong.to.us>
Date: Mon, 19 Feb 2024 14:03:18 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Samuel Holland <samuel.holland@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, Samuel
 Holland <samuel.holland@...ive.com>
Subject: Re: [PATCH 4/7] riscv: Simplify text patching loops

Samuel Holland <samuel.holland@...ive.com> writes:

> This reduces the number of variables and makes the code easier to parse.
>
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
>
>  arch/riscv/kernel/patch.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index bccd9ed04a05..7f030b46eae5 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -155,7 +155,6 @@ NOKPROBE_SYMBOL(__patch_insn_write);
>  
>  static int patch_insn_set(void *addr, u8 c, size_t len)
>  {
> -	size_t patched = 0;
>  	size_t size;
>  	int ret = 0;
>  
> @@ -163,11 +162,12 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
>  	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
>  	 * loop with len <= 2 * PAGE_SIZE.
>  	 */
> -	while (patched < len && !ret) {
> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> -		ret = __patch_insn_set(addr + patched, c, size);
> +	while (len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
> +		ret = __patch_insn_set(addr, c, size);

While you're at it, do:
  ret = __patch_insn_set(addr, c, size);
  if (ret)
          return ret;
  ...
return 0;
}

and simplify the while-loop predicate?

>  
> -		patched += size;
> +		addr += size;
> +		len -= size;
>  	}
>  
>  	return ret;
> @@ -190,7 +190,6 @@ NOKPROBE_SYMBOL(patch_text_set_nosync);
>  
>  int patch_insn_write(void *addr, const void *insn, size_t len)
>  {
> -	size_t patched = 0;
>  	size_t size;
>  	int ret = 0;
>  
> @@ -198,11 +197,13 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
>  	 * Copy the instructions to the destination address, two pages at a time
>  	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
>  	 */
> -	while (patched < len && !ret) {
> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> -		ret = __patch_insn_write(addr + patched, insn + patched, size);
> +	while (len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
> +		ret = __patch_insn_write(addr, insn, size);

Same comment as above.


Björn