linux-kernel - Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent instrumentation inserted

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Date:   Thu, 8 Sep 2022 09:33:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     guoren@...nel.org
Cc:     arnd@...db.de, palmer@...osinc.com, tglx@...utronix.de,
        luto@...nel.org, conor.dooley@...rochip.com, heiko@...ech.de,
        jszhang@...nel.org, lazyparser@...il.com, falcon@...ylab.org,
        chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, bigeasy@...utronix.de,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent
 instrumentation inserted

On Wed, Sep 07, 2022 at 10:25:02PM -0400, guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
> 
> Without noinstr the compiler is free to insert instrumentation (think
> all the k*SAN, KCov, GCov, ftrace etc..) which can call code we're not
> yet ready to run this early in the entry path, for instance it could
> rely on RCU which isn't on yet, or expect lockdep state. (by peterz)
> 
> Link: https://lore.kernel.org/linux-riscv/YxcQ6NoPf3AH0EXe@hirez.programming.kicks-ass.net/raw
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> ---
>  arch/riscv/kernel/traps.c | 8 ++++----
>  arch/riscv/mm/fault.c     | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 635e6ec26938..3ed3dbec250d 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -97,7 +97,7 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code,
>  #define __trap_section
>  #endif
>  #define DO_ERROR_INFO(name, signo, code, str)				\
> -asmlinkage __visible __trap_section void name(struct pt_regs *regs)	\
> +asmlinkage __visible __trap_section void noinstr name(struct pt_regs *regs)	\

But now you have __trap_section and noinstr both adding a section
attribute.