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Wed, 28 Oct 2020 07:17:50 -0400 X-MC-Unique: 5Kg-MYA4O2aB4WCrNYOgXA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 90BEC809DE4; Wed, 28 Oct 2020 11:17:44 +0000 (UTC) Received: from [10.36.114.138] (ovpn-114-138.ams2.redhat.com [10.36.114.138]) by smtp.corp.redhat.com (Postfix) with ESMTP id 033EC6EF5E; Wed, 28 Oct 2020 11:17:35 +0000 (UTC) Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation To: Mike Rapoport Cc: "Edgecombe, Rick P" , "cl@linux.com" , "gor@linux.ibm.com" , "hpa@zytor.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "borntraeger@de.ibm.com" , "penberg@kernel.org" , "linux-mm@kvack.org" , "iamjoonsoo.kim@lge.com" , "will@kernel.org" , "aou@eecs.berkeley.edu" , "kirill@shutemov.name" , "rientjes@google.com" , "rppt@linux.ibm.com" , "paulus@samba.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "pavel@ucw.cz" , "sparclinux@vger.kernel.org" , "akpm@linux-foundation.org" , "luto@kernel.org" , "davem@davemloft.net" , "mpe@ellerman.id.au" , "benh@kernel.crashing.org" , "linuxppc-dev@lists.ozlabs.org" , "rjw@rjwysocki.net" , "tglx@linutronix.de" , "linux-riscv@lists.infradead.org" , "x86@kernel.org" , "linux-pm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "palmer@dabbelt.com" , "Brown, Len" , "mingo@redhat.com" , "linux-s390@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "paul.walmsley@sifive.com" References: <20201025101555.3057-1-rppt@kernel.org> <20201026090526.GA1154158@kernel.org> <20201027083816.GG1154158@kernel.org> <20201028110945.GE1428094@kernel.org> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <5805fdd9-14e5-141c-773b-c46d2da57258@redhat.com> Date: Wed, 28 Oct 2020 12:17:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201028110945.GE1428094@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 28.10.20 12:09, Mike Rapoport wrote: > 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? > Clould be! Also see https://lkml.kernel.org/r/38de5bb0-5559-d069-0ce0-daec66ef2746@suse.cz which restores free page content based on more kernel parameters, not based on the original content. -- Thanks, David / dhildenb