linux-kernel - Re: [PATCH] mm: Generalize and rename notify_page_fault() as kprobe_page

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Date:   Fri, 14 Jun 2019 10:45:44 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        x86@...nel.org, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        James Hogan <jhogan@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH] mm: Generalize and rename notify_page_fault() as
 kprobe_page_fault()


On 06/14/2019 01:34 AM, Andrew Morton wrote:
> On Thu, 13 Jun 2019 15:37:24 +0530 Anshuman Khandual <anshuman.khandual@....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?

Matthew had suggested that (nokprobe_-inline) based on current x86
implementation. But every architecture already had an inlined definition
which I did not want to deviate from.

> 
> 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.

I would believe so. No one has complained yet :)