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

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Date:   Fri, 5 Aug 2022 16:27:40 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Rik van Riel <riel@...riel.com>
Cc:     Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v3] x86,mm: print likely CPU at segfault time

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.

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