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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 583F2C4363A for ; Wed, 28 Oct 2020 11:16:02 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C1F81246B2 for ; Wed, 28 Oct 2020 11:15:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="rSkA1LMT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C1F81246B2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4CLmGN504qzDqSP for ; Wed, 28 Oct 2020 22:15:56 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=198.145.29.99; helo=mail.kernel.org; envelope-from=rppt@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=rSkA1LMT; dkim-atps=neutral Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4CLm7b02klzDqNL for ; Wed, 28 Oct 2020 22:10:02 +1100 (AEDT) Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E673E246A2; Wed, 28 Oct 2020 11:09:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603883399; bh=eCXz+icsPBbUt7e5/gqYfjD87B/R7/XDnyNtNoyBXrk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rSkA1LMThGYa8UMoSh4pNOLlYk0Lxh/6LDfGk3lRhOIkmwmSNIL5gi4KdTIE8Tsxu qd8mkHa8sLSEDYsQV8mEhfTUE/HscCn3fQbHDAv2vipDt0prchwp0fFl1i7QNwuZ5Y aIHs1RviptzndqpoN78OxdW+Os4KYEQl9gh6FnDI= Date: Wed, 28 Oct 2020 13:09:45 +0200 From: Mike Rapoport To: David Hildenbrand Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Message-ID: <20201028110945.GE1428094@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201026090526.GA1154158@kernel.org> <20201027083816.GG1154158@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "iamjoonsoo.kim@lge.com" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "akpm@linux-foundation.org" , "Edgecombe, Rick P" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Oct 27, 2020 at 09:46:35AM +0100, David Hildenbrand wrote: > On 27.10.20 09:38, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 06:05:30PM +0000, Edgecombe, Rick P wrote: > > > > > Beyond whatever you are seeing, for the latter case of new things > > > getting introduced to an interface with hidden dependencies... Another > > > edge case could be a new caller to set_memory_np() could result in > > > large NP pages. None of the callers today should cause this AFAICT, but > > > it's not great to rely on the callers to know these details. > > A caller of set_memory_*() or set_direct_map_*() should expect a failure > > and be ready for that. So adding a WARN to safe_copy_page() is the first > > step in that direction :) > > > > I am probably missing something important, but why are we saving/restoring > the content of pages that were explicitly removed from the identity mapping > such that nobody will access them? Actually, we should not be saving/restoring free pages during hibernation as there are several calls to mark_free_pages() that should exclude the free pages from the snapshot. I've tried to find why the fix that maps/unmaps a page to save it was required at the first place, but I could not find bug reports. The closest I've got is an email from Rafael that asked to update "hibernate: handle DEBUG_PAGEALLOC" patch: https://lore.kernel.org/linux-pm/200802200133.44098.rjw@sisk.pl/ Could it be that safe_copy_page() tries to workaround a non-existent problem? -- Sincerely yours, Mike.