linux-kernel - Re: [PATCH v8 17/22] arm64: mm: Add page fault trace points

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Message-ID: <aCtE-RvyN6XJQjTo@arm.com>
Date: Mon, 19 May 2025 15:49:29 +0100
From: Catalin Marinas <catalin.marinas@....com>
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, Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 17/22] arm64: mm: Add page fault trace points

On Mon, May 12, 2025 at 12:51:00PM +0200, Nam Cao wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index ec0a337891dd..55094030e377 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);
> @@ -559,6 +562,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  	if (kprobe_page_fault(regs, esr))
>  		return 0;
>  
> +	if (user_mode(regs))
> +		trace_page_fault_user(addr, regs, esr);
> +	else
> +		trace_page_fault_kernel(addr, regs, esr);

What are the semantics for these tracepoints? When are they supposed to
be called? In the RV context context I guess you only care about the
benign, recoverable faults that would affect timing. These tracepoints
were generalised from the x86 code but I don't know enough about it to
tell when they would be invoked.

For arm64, we also have the do_translation_fault() path for example that
may or may not need to log such trace events.

-- 
Catalin