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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 21BFBC2D0A3 for ; Mon, 26 Oct 2020 09:05:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C593822403 for ; Mon, 26 Oct 2020 09:05:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603703145; bh=qV1j3o8b5aO+jtdBDoJyX5701vJJcUPPuK5bWgUroMs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=xujcdi2/7QvTewImrWw6/TfULRogxOPI1s9XpCjQxLk5XCAvBrua2HC+b4ThTU01u /UinNhsgTJxUNfLecP90jEWdfzn2EqX+OAHGlI60V2uxAX/o+xa7O7TrvIkiMH3KS5 DZGCDOk6xCtrnDXVh/FFUQgPjeSCIzm0m/Yf47NA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1772545AbgJZJFp (ORCPT ); Mon, 26 Oct 2020 05:05:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:58514 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390998AbgJZJFo (ORCPT ); Mon, 26 Oct 2020 05:05:44 -0400 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 4F28122242; Mon, 26 Oct 2020 09:05:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603703144; bh=qV1j3o8b5aO+jtdBDoJyX5701vJJcUPPuK5bWgUroMs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n6pQeRtZ1dQZQwNLzcRvocBVxWOThQ2A3ohdsbB1ku0q9Z1z2DOVNvIaiR/xbrSRK 5zQtm2aEbLsKv3mU1aC9GYppS4t99gNCuK2wQoR74ofGRKXtqAOsYTKvXA+WFU2Lid njOARSpftIz0V7Pd9Gh+IjN51p6qFKYl2MBmmm2s= Date: Mon, 26 Oct 2020 11:05:26 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Cc: "akpm@linux-foundation.org" , "david@redhat.com" , "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" , "will@kernel.org" , "penberg@kernel.org" , "iamjoonsoo.kim@lge.com" , "aou@eecs.berkeley.edu" , "kirill@shutemov.name" , "rientjes@google.com" , "rppt@linux.ibm.com" , "paulus@samba.org" , "hca@linux.ibm.com" , "pavel@ucw.cz" , "bp@alien8.de" , "sparclinux@vger.kernel.org" , "mpe@ellerman.id.au" , "luto@kernel.org" , "davem@davemloft.net" , "linux-mm@kvack.org" , "tglx@linutronix.de" , "rjw@rjwysocki.net" , "linux-riscv@lists.infradead.org" , "benh@kernel.crashing.org" , "linuxppc-dev@lists.ozlabs.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" Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Message-ID: <20201026090526.GA1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Mon, Oct 26, 2020 at 01:13:52AM +0000, Edgecombe, Rick P wrote: > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP > > it is > > possible that __kernel_map_pages() would fail, but since this > > function is > > void, the failure will go unnoticed. > > Could you elaborate on how this could happen? Do you mean during > runtime today or if something new was introduced? A failure in__kernel_map_pages() may happen today. For instance, on x86 if the kernel is built with DEBUG_PAGEALLOC. __kernel_map_pages(page, 1, 0); will need to split, say, 2M page and during the split an allocation of page table could fail. Currently, the only user of __kernel_map_pages() outside DEBUG_PAGEALLOC is hibernation, but I think it would be safer to entirely prevent usage of __kernel_map_pages() when DEBUG_PAGEALLOC=n. -- Sincerely yours, Mike.