linux-kernel - Re: [PATCH v9 17/22] arm64: mm: Add page fault trace points

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Message-ID: <aG0aIKzxApp9j7X0@willie-the-truck>
Date: Tue, 8 Jul 2025 14:16:16 +0100
From: Will Deacon <will@...nel.org>
To: Nam Cao <namcao@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Gabriele Monaco <gmonaco@...hat.com>,
	linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
	john.ogness@...utronix.de,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 17/22] arm64: mm: Add page fault trace points

On Mon, May 19, 2025 at 12:27:35PM +0200, Nam Cao wrote:
> Add page fault trace points, which are useful to implement RV monitor which
> watches page faults.
> 
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
>  arch/arm64/mm/fault.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index ec0a337891dd..d917556869f9 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -44,6 +44,9 @@
>  #include <asm/tlbflush.h>
>  #include <asm/traps.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/exceptions.h>
> +
>  struct fault_info {
>  	int	(*fn)(unsigned long far, unsigned long esr,
>  		      struct pt_regs *regs);
> @@ -556,6 +559,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  	int si_code;
>  	int pkey = -1;
>  
> +	if (user_mode(regs))
> +		trace_page_fault_user(addr, regs, esr);
> +	else
> +		trace_page_fault_kernel(addr, regs, esr);
> +
>  	if (kprobe_page_fault(regs, esr))
>  		return 0;

As per the discussion with Steve on v6, I still object to relying on the
arch code to call all these different trace helpers (rv, kprobes, perf)
in the right place and consistently with each other.

In:

https://lore.kernel.org/r/20250519120837.794f6738@batman.local.home

Steve suggested wrapping some of this up in a core function to help with
that.

Will