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| From | Ingo Molnar <mingo@kernel.org> |
| Newsgroups | linux.kernel |
| Subject | Re: why do we need vmalloc_sync_all? |
| Date | Mon, 15 Jun 2015 22:30:03 +0200 |
| Message-ID | <pBJb5-5IV-29@gated-at.bofh.it> (permalink) |
| References | <pAQeC-Ge-7@gated-at.bofh.it> <pAYOS-4Iu-1@gated-at.bofh.it> <pBb9n-6cY-3@gated-at.bofh.it> <pBmo9-6xN-3@gated-at.bofh.it> <pBsDf-6ZX-1@gated-at.bofh.it> <pBsMW-7b9-15@gated-at.bofh.it> |
| X-Original-To | Andy Lutomirski <luto@amacapital.net> |
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| X-Original-Cc | Andi Kleen <andi@firstfloor.org>, Oleg Nesterov <oleg@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>, Linus Torvalds <torvalds@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Waiman Long <Waiman.Long@hp.com> |
| X-Original-Date | Mon, 15 Jun 2015 22:28:57 +0200 |
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| X-Original-References | <1434188955-31397-1-git-send-email-mingo@kernel.org> <20150613185828.GA32376@redhat.com> <20150614075943.GA810@gmail.com> <20150614200623.GB19582@redhat.com> <87bnghit74.fsf@tassilo.jf.intel.com> <CALCETrUp5Xm1ZmzoSEGrq1D05myAUhCzNgXvv-Cga8xjEi-CeQ@mail.gmail.com> |
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| Xref | aioe.org linux.kernel:1165537 |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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Re: why do we need vmalloc_sync_all? Oleg Nesterov <oleg@redhat.com> - 2015-06-14 22:10 +0200
Re: why do we need vmalloc_sync_all? Ingo Molnar <mingo@kernel.org> - 2015-06-15 22:30 +0200
Re: why do we need vmalloc_sync_all? Andy Lutomirski <luto@amacapital.net> - 2015-06-15 22:50 +0200
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