linux-kernel - Re: [PATCH 37/49] x86/alternatives: Move text_poke_array completion from smp_text_poke_batch_finish() and smp_text_poke_batch_flush() to smp_text_poke_batch

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Message-ID: <Z-6pQPDuNkshB04F@gmail.com>
Date: Thu, 3 Apr 2025 17:29:04 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: linux-kernel@...r.kernel.org, Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 37/49] x86/alternatives: Move text_poke_array completion
 from smp_text_poke_batch_finish() and smp_text_poke_batch_flush() to
 smp_text_poke_batch_process()


* Nikolay Borisov <nik.borisov@...e.com> wrote:

> I meant doing this:
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 5b1a6252a4b9..b6a781b9de26 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -2587,12 +2587,16 @@ noinstr int smp_text_poke_int3_trap_handler(struct
> pt_regs *regs)
>   *               replacing opcode
>   *     - SMP sync all CPUs
>   */
> -static void smp_text_poke_batch_process(void)
> +void smp_text_poke_batch_finish(void)
>  {
>         unsigned char int3 = INT3_INSN_OPCODE;
>         unsigned int i;
>         int do_sync;
> 
> +
> +       if (!text_poke_array.nr_entries)
> +               return;

> -               smp_text_poke_batch_process();
> +               smp_text_poke_batch_finish();

I suppose we could do this - it adds one more check to 
smp_text_poke_batch_add() though.

> AFAICS this doesn't change the semantics. I.e smp_text_poke_batch_add 
> will call poke_batch_finish iff the address to be added violates the 
> sorted order of text_poke_array. The net effect is we have 1 less 
> function name to care about.

Yeah, it doesn't change semantics, but it's a very small 
deoptimization.

Mind sending a patch? It does simplify the facility some more and that 
single branch will wash away against costs like the CR3 flushes done 
...

Thanks,

	Ingo