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

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Message-ID: <20250520122548.lkvaylSB@linutronix.de>
Date: Tue, 20 May 2025 14:25:48 +0200
From: Nam Cao <namcao@...utronix.de>
To: Catalin Marinas <catalin.marinas@....com>
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 19, 2025 at 03:49:29PM +0100, Catalin Marinas wrote:
> 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.

These tracepoints are invoked for x86 page fault exceptions. Are arm64's
translation faults considered equivalent to x86 page faults?

Best regards,
Nam