linux-kernel - Re: [PATCH] x86: add hintable NOPs emulation

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Message-ID: <aKWj0SI1_qmT6dW2@lx-t490>
Date: Wed, 20 Aug 2025 12:30:41 +0200
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Marcos Del Sol Vives <marcos@...a.pet>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	Uros Bizjak <ubizjak@...il.com>, Ard Biesheuvel <ardb@...nel.org>,
	David Kaplan <david.kaplan@....com>, Kees Cook <kees@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Oleg Nesterov <oleg@...hat.com>, "Xin Li (Intel)" <xin@...or.com>,
	Sabyrzhan Tasbolatov <snovitoll@...il.com>
Subject: Re: [PATCH] x86: add hintable NOPs emulation

On Wed, 20 Aug 2025, Ahmed S. Darwish wrote:
>
> Please do:
>
>     #ifdef CONFIG_X86_HNOP_EMU
>     static bool handle_hnop(struct pt_regs *regs)
>     {
> 	// Reference 'hnop_warn' as much as you like
>     }
>     #else
>     static bool handle_hnop(struct pt_regs *regs)
>     {
> 	return false;
>     }
>     # endif
>

And as previously suggested: remove the ugly hnop_warn stuff from
'thread_struct', then you can even just do:

    static bool handle_hnop(struct pt_regs *regs)
    {
	if (!IS_ENABLED(CONFIG_X86_HNOP_EMU))
		return false;

	pr_warn_once("%s[%d] Emulating hintable NOP\n"
		     "This warning will not be repeated; even for other binaries\n"
		     current->comm, task_pid_nr(current));

	...
    }

And everything else will fit quietly in place.

--
Ahmed S. Darwish
Linutronix GmbH