Messages in this thread | | | Date | Mon, 15 Jun 2015 22:28:57 +0200 | From | Ingo Molnar <> | Subject | Re: why do we need vmalloc_sync_all? |
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* Andy Lutomirski <luto@amacapital.net> wrote:
> On Sun, Jun 14, 2015 at 7:47 PM, Andi Kleen <andi@firstfloor.org> wrote: > > Oleg Nesterov <oleg@redhat.com> 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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