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

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Message-ID: <e5f45089-c3aa-4d78-2c8d-ed22f863d9ee@synopsys.com>
Date:   Thu, 13 Jun 2019 10:57:45 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
CC:     Mark Rutland <mark.rutland@....com>,
        Michal Hocko <mhocko@...e.com>, <linux-ia64@...r.kernel.org>,
        <linux-sh@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        Will Deacon <will.deacon@....com>,
        Paul Mackerras <paulus@...ba.org>,
        <sparclinux@...r.kernel.org>,
        "Stephen Rothwell" <sfr@...b.auug.org.au>,
        <linux-s390@...r.kernel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michael Ellerman <mpe@...erman.id.au>, <x86@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        James Hogan <jhogan@...nel.org>,
        <linux-snps-arc@...ts.infradead.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        Thomas Gleixner <tglx@...opsys.com>,
        "Masami Hiramatsu" <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH] mm: Generalize and rename notify_page_fault() as
 kprobe_page_fault()

+CC Masami San

On 6/13/19 3:07 AM, Anshuman Khandual wrote:
> Questions:
> 
> AFAICT there is no equivalent of erstwhile notify_page_fault() during page
> fault handling in arc and mips archs which can call this generic function.
> Please let me know if that is not the case.

For ARC do_page_fault() is entered for MMU exceptions (TLB Miss, access violations
r/w/x etc). kprobes uses a combination of UNIMP_S and TRAP_S instructions which
don't funnel into do_page_fault().

UINMP_S leads to

instr_service
   do_insterror_or_kprobe
      notify_die(DIE_IERR)
         kprobe_exceptions_notify
            arc_kprobe_handler


TRAP_S 2 leads to

EV_Trap
   do_non_swi_trap
      trap_is_kprobe
         notify_die(DIE_TRAP)
            kprobe_exceptions_notify
               arc_post_kprobe_handler

But indeed we are *not* calling into kprobe_fault_handler() - from eithet of those
paths and not sure if the existing arc*_kprobe_handler() combination does the
equivalent in tandem.

-Vineet