linux-kernel - Re: [PATCH 23/49] x86/alternatives: Simplify smp_text_poke_single() by using tp

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Message-ID: <20250401144010.GJ5880@noisy.programming.kicks-ass.net>
Date: Tue, 1 Apr 2025 16:40:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 23/49] x86/alternatives: Simplify smp_text_poke_single()
 by using tp_vec and existing APIs

On Fri, Mar 28, 2025 at 02:26:38PM +0100, Ingo Molnar wrote:
> Instead of constructing a vector on-stack, just use the already
> available batch-patching vector - which should always be empty
> at this point.
> 
> This will allow subsequent simplifications.

This should go before patch 20, otherwise you'll have this intermediate
state where we trip the WARN, no?

> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/kernel/alternative.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index ffffec4597b7..70abc636b87c 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -2906,8 +2906,13 @@ void __ref smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, c
>   */
>  void __ref smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate)
>  {
> -	struct smp_text_poke_loc tp;
> +	struct smp_text_poke_loc *tp;
> +
> +	/* Batch-patching should not be mixed with single-patching: */
> +	WARN_ON_ONCE(tp_vec_nr != 0);
> +
> +	tp = &tp_vec[tp_vec_nr++];
> +	text_poke_int3_loc_init(tp, addr, opcode, len, emulate);
>  
> -	text_poke_int3_loc_init(&tp, addr, opcode, len, emulate);
> -	smp_text_poke_batch_process(&tp, 1);
> +	smp_text_poke_batch_finish();
>  }
> -- 
> 2.45.2
>