Re: [PATCH] mm: Generalize and rename notify_page_fault() as kprobe_page_fault()

From: Andrew Morton <akpm@linux-foundation.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org,
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	Matthew Wilcox <willy@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
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	Andrey Konovalov <andreyknvl@google.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
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	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
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	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Vineet Gupta <vgupta@synopsys.com>,
	James Hogan <jhogan@kernel.org>,
	Paul Burton <paul.burton@mips.com>,
	Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] mm: Generalize and rename notify_page_fault() as kprobe_page_fault()
Date: Thu, 13 Jun 2019 13:04:08 -0700	[thread overview]
Message-ID: <20190613130408.3091869d8e50d0524157523f@linux-foundation.org> (raw)
In-Reply-To: <1560420444-25737-1-git-send-email-anshuman.khandual@arm.com>

On Thu, 13 Jun 2019 15:37:24 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:

> Architectures which support kprobes have very similar boilerplate around
> calling kprobe_fault_handler(). Use a helper function in kprobes.h to unify
> them, based on the x86 code.
> 
> This changes the behaviour for other architectures when preemption is
> enabled. Previously, they would have disabled preemption while calling the
> kprobe handler. However, preemption would be disabled if this fault was
> due to a kprobe, so we know the fault was not due to a kprobe handler and
> can simply return failure.
> 
> This behaviour was introduced in the commit a980c0ef9f6d ("x86/kprobes:
> Refactor kprobes_fault() like kprobe_exceptions_notify()")
> 
> ...
>
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -30,28 +30,6 @@
>  
>  #ifdef CONFIG_MMU
>  
> -#ifdef CONFIG_KPROBES
> -static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr)

Some architectures make this `static inline'.  Others make it
`nokprobes_inline', others make it `static inline __kprobes'.  The
latter seems weird - why try to put an inline function into
.kprobes.text?

So..  what's the best thing to do here?  You chose `static
nokprobe_inline' - is that the best approach, if so why?  Does
kprobe_page_fault() actually need to be inlined?

Also, some architectures had notify_page_fault returning int, others
bool.  You chose bool and that seems appropriate and all callers are OK
with that.