* Andy Lutomirski <[email protected]> wrote:
> On Sun, Jun 14, 2015 at 7:47 PM, Andi Kleen <[email protected]> wrote:
> > Oleg Nesterov <[email protected]> writes:
> >>
> >> But again, the kernel no longer does this? do_page_fault() does
> >> vmalloc_fault() without notify_die(). If it fails, I do not see how/why a
> >> modular DIE_OOPS handler could try to resolve this problem and trigger
> >> another fault.
> >
> > The same problem can happen from NMI handlers or machine check handlers.
> > It's
> > not necessarily tied to page faults only.
>
> AIUI, the point of the one and only vmalloc_sync_all call is to prevent
> infinitely recursive faults when we call a notify_die callback. The only
> thing
> that it could realistically protect is module text or static non-per-cpu
> module
> data, since that's the only thing that's reliably already in the init pgd.
> I'm
> with Oleg: I don't see how that can happen, since do_page_fault fixes up
> vmalloc
> faults before it calls notify_die.
Yes, but what I meant is that it can happen if due to an unrelated kernel bug
and
unlucky timing we have installed this new handler just when that other
unrelated
kernel bug triggers: say a #GPF crash in kernel code.
In any case it should all be mooted with the removal of lazy PGD instantiation.
Thanks,
Ingo
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