Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753365AbbFOC6R (ORCPT ); Sun, 14 Jun 2015 22:58:17 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:32811 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752368AbbFOC6K (ORCPT ); Sun, 14 Jun 2015 22:58:10 -0400 MIME-Version: 1.0 In-Reply-To: <87bnghit74.fsf@tassilo.jf.intel.com> 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> From: Andy Lutomirski Date: Sun, 14 Jun 2015 19:57:46 -0700 Message-ID: Subject: Re: why do we need vmalloc_sync_all? To: Andi Kleen Cc: Oleg Nesterov , Ingo Molnar , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Andrew Morton , Denys Vlasenko , Brian Gerst , Peter Zijlstra , Borislav Petkov , "H. Peter Anvin" , Linus Torvalds , Thomas Gleixner , Waiman Long Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1159 Lines: 24 On Sun, Jun 14, 2015 at 7:47 PM, Andi Kleen wrote: > Oleg Nesterov 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. --Andy -- 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/