From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08AA4C433ED for ; Tue, 18 May 2021 10:31:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFE2C61002 for ; Tue, 18 May 2021 10:31:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348438AbhERKcd (ORCPT ); Tue, 18 May 2021 06:32:33 -0400 Received: from mx2.suse.de ([195.135.220.15]:40952 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347898AbhERKca (ORCPT ); Tue, 18 May 2021 06:32:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1621333869; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=11zOMNPLAXlfQ0IrA6mDqgUqLx9G4ocdGPmWlci12vs=; b=bCoq0/YrkDVfJ7aWUPtL/xVkLxy11Ug+HfDnAxDrJFs7J6MgrDlXYRSDS7vwtswRGIHJJl uObdMarvUwYFhAdiJHuWUmf5YEujX5yzqduBIhu8Ofk+r5f5M4cJzTltdLBU5nTztdSQFT kY0Rtk5Y/SQujsAoM5OCY/XuAUnk3fA= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 99DFCAFEC; Tue, 18 May 2021 10:31:09 +0000 (UTC) Date: Tue, 18 May 2021 12:31:08 +0200 From: Michal Hocko To: David Hildenbrand Cc: Mike Rapoport , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Hagen Paul Pfeifer , Ingo Molnar , James Bottomley , Kees Cook , "Kirill A. Shutemov" , Matthew Wilcox , Matthew Garrett , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , "Rafael J. Wysocki" , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , Yury Norov , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org Subject: Re: [PATCH v19 5/8] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: References: <20210513184734.29317-1-rppt@kernel.org> <20210513184734.29317-6-rppt@kernel.org> <8e114f09-60e4-2343-1c42-1beaf540c150@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8e114f09-60e4-2343-1c42-1beaf540c150@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue 18-05-21 12:06:42, David Hildenbrand wrote: > On 18.05.21 11:59, Michal Hocko wrote: > > On Sun 16-05-21 10:29:24, Mike Rapoport wrote: > > > On Fri, May 14, 2021 at 11:25:43AM +0200, David Hildenbrand wrote: > > [...] > > > > > + if (!page) > > > > > + return VM_FAULT_OOM; > > > > > + > > > > > + err = set_direct_map_invalid_noflush(page, 1); > > > > > + if (err) { > > > > > + put_page(page); > > > > > + return vmf_error(err); > > > > > > > > Would we want to translate that to a proper VM_FAULT_..., which would most > > > > probably be VM_FAULT_OOM when we fail to allocate a pagetable? > > > > > > That's what vmf_error does, it translates -ESOMETHING to VM_FAULT_XYZ. > > > > I haven't read through the rest but this has just caught my attention. > > Is it really reasonable to trigger the oom killer when you cannot > > invalidate the direct mapping. From a quick look at the code it is quite > > unlikely to se ENOMEM from that path (it allocates small pages) but this > > can become quite sublte over time. Shouldn't this simply SIGBUS if it > > cannot manipulate the direct mapping regardless of the underlying reason > > for that? > > > > OTOH, it means our kernel zones are depleted, so we'd better reclaim somehow > ... Killing a userspace seems to be just a bad way around that. Although I have to say openly that I am not a great fan of VM_FAULT_OOM in general. It is usually a a wrong way to tell the handle the failure because it happens outside of the allocation context so you lose all the details (e.g. allocation constrains, numa policy etc.). Also whenever there is ENOMEM then the allocation itself has already made sure that all the reclaim attempts have been already depleted. Just consider an allocation with GFP_NOWAIT/NO_RETRY or similar to fail and propagate ENOMEM up the call stack. Turning that into the OOM killer sounds like a bad idea to me. But that is a more general topic. I have tried to bring this up in the past but there was not much of an interest to fix it as it was not a pressing problem... -- Michal Hocko SUSE Labs