linux-kernel - Re: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation

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Date:   Fri, 8 May 2020 22:27:50 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation

On Tue, 05 May 2020 15:49:28 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> From: Peter Zijlstra <peterz@...radead.org>
> 
> Use arch_atomic_*() and READ_ONCE_NOCHECK() to ensure nothing untoward
> creeps in and ruins things.
> 
> That is; this is the INT3 text poke handler, strictly limit the code
> that runs in it, lest it inadvertenly hits yet another INT3.
> 
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

> ---
>  arch/x86/kernel/alternative.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -960,9 +960,9 @@ static struct bp_patching_desc *bp_desc;
>  static __always_inline
>  struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
>  {
> -	struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
> +	struct bp_patching_desc *desc = READ_ONCE_NOCHECK(*descp); /* rcu_dereference */
>  
> -	if (!desc || !atomic_inc_not_zero(&desc->refs))
> +	if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
>  		return NULL;
>  
>  	return desc;
> @@ -971,7 +971,7 @@ struct bp_patching_desc *try_get_desc(st
>  static __always_inline void put_desc(struct bp_patching_desc *desc)
>  {
>  	smp_mb__before_atomic();
> -	atomic_dec(&desc->refs);
> +	arch_atomic_dec(&desc->refs);
>  }
>  
>  static __always_inline void *text_poke_addr(struct text_poke_loc *tp)
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>