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

Masami Hiramatsu
2019-06-20T07:19:17Z

Hi,

On Tue, 18 Jun 2019 08:56:33 -0700
Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:

> +CC Masami San, Eugeniy
>
> On 6/13/19 10:57 AM, Vineet Gupta wrote:
>
>
> > 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.

Interesting, it seems that the kprobe_fault_handler() has never been called.
Anyway, it is used for handling a page fault in kprobe's user handler or single
stepping. And a page fault in user handler will not hard to fix up. Only a hard
case is a page fault in single stepping. If ARC's kprobes using single-stepping
on copied buffer, it may crashes kernel, since fixup code can not find correct
address without kprobe_fault_handler.

Thank you,

>
> @Eugeniy can you please investigate this - do we have krpobes bit rot in ARC port.
>
> -Vineet
>
>

--
Masami Hiramatsu <mhiramat@kernel.org>