linux-kernel - Re: [PATCH -fixes] riscv: patch: Flush the icache right after patching to avoid illegal insns

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Message-ID: <CAMuHMdUwx=rU2MWhFTE6KhYHm64phxx2Y6u05-aBLGfeG5696A@mail.gmail.com>
Date: Tue, 9 Jul 2024 10:13:12 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Björn Töpel <bjorn@...osinc.com>, 
	Andy Chiu <andy.chiu@...ive.com>, Puranjay Mohan <puranjay12@...il.com>, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH -fixes] riscv: patch: Flush the icache right after
 patching to avoid illegal insns

Hi Alexandre,

On Mon, Jun 24, 2024 at 10:23 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
> We cannot delay the icache flush after patching some functions as we may
> have patched a function that will get called before the icache flush.
>
> The only way to completely avoid such scenario is by flushing the icache
> as soon as we patch a function. This will probably be costly as we don't
> batch the icache maintenance anymore.
>
> Fixes: 6ca445d8af0e ("riscv: Fix early ftrace nop patching")
> Reported-by: Conor Dooley <conor.dooley@...rochip.com>
> Closes: https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks for your patch, which is now commit edf2d546bfd6f5c4 ("riscv:
patch: Flush the icache right after patching to avoid illegal
insns") in v6.10-rc6.

> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -189,9 +205,6 @@ int patch_text_set_nosync(void *addr, u8 c, size_t len)
>
>         ret = patch_insn_set(tp, c, len);
>
> -       if (!ret)
> -               flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
> -
>         return ret;
>  }
>  NOKPROBE_SYMBOL(patch_text_set_nosync);

patch_text_set_nosync() is now identical to (static) patch_insn_set(),
and the latter has no other callers.

> @@ -224,9 +237,6 @@ int patch_text_nosync(void *addr, const void *insns, size_t len)
>
>         ret = patch_insn_write(tp, insns, len);
>
> -       if (!ret)
> -               flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
> -
>         return ret;
>  }
>  NOKPROBE_SYMBOL(patch_text_nosync);

patch_text_nosync() is now identical to patch_insn_write(), and both
functions are called from outside this file.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds