Re: [PATCH v3] x86,mm: print likely CPU at segfault time

From: Borislav Petkov <bp@alien8.de>
To: Rik van Riel <riel@surriel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com,
	Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v3] x86,mm: print likely CPU at segfault time
Date: Fri, 5 Aug 2022 16:27:40 +0200	[thread overview]
Message-ID: <Yu0o3J2T5QwKtoan@zn.tnic> (raw)
In-Reply-To: <20220805101644.2e674553@imladris.surriel.com>

On Fri, Aug 05, 2022 at 10:16:44AM -0400, Rik van Riel wrote:
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index fad8faa29d04..c7a5bbf40367 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -769,6 +769,8 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
>  		unsigned long address, struct task_struct *tsk)
>  {
>  	const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
> +	/* This is a racy snapshot, but it's better than nothing. */
> +	int cpu = raw_smp_processor_id();

Please read this in exc_page_fault() and hand it down to helpers.

Alternatively, I'm being told there's a patchset in the works which
will allow for any exception handler to pass in additional information
downwards through an extended pt_regs. Then, saving the CPU number on
which the handler is running would work generically everywhere.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette