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=-0.8 required=3.0 tests=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 CC687C433E0 for ; Wed, 13 May 2020 16:21:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 19F6E2054F for ; Wed, 13 May 2020 16:21:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389437AbgEMQVw (ORCPT ); Wed, 13 May 2020 12:21:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732296AbgEMQVw (ORCPT ); Wed, 13 May 2020 12:21:52 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3ED88C061A0C; Wed, 13 May 2020 09:21:52 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jYu8a-0000Aq-B5; Wed, 13 May 2020 18:21:40 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id BFC37100605; Wed, 13 May 2020 18:21:39 +0200 (CEST) From: Thomas Gleixner To: Alan Stern Cc: Greg KH , syzbot , bp@alien8.de, dave.hansen@linux.intel.com, dmitry.torokhov@gmail.com, ebiederm@xmission.com, hpa@zytor.com, jeremy.linton@arm.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, luto@kernel.org, mingo@redhat.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, x86@kernel.org Subject: Re: WARNING in memtype_reserve In-Reply-To: References: Date: Wed, 13 May 2020 18:21:39 +0200 Message-ID: <8736833iwc.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alan Stern writes: > On Sat, 9 May 2020, Thomas Gleixner wrote: > >> Greg KH writes: >> > On Sat, May 09, 2020 at 12:20:14AM -0700, syzbot wrote: >> >> memtype_reserve failed: [mem 0xffffffffff000-0x00008fff], req write-back >> >> WARNING: CPU: 1 PID: 7025 at arch/x86/mm/pat/memtype.c:589 memtype_reserve+0x69f/0x820 arch/x86/mm/pat/memtype.c:589 >> > >> > So should memtype_reserve() not do a WARN if given invalid parameters as >> > it can be triggered by userspace requests? >> > >> > A normal "invalid request" debug line is probably all that is needed, >> > right? >> >> I disagree. The callsite espcially if user space triggerable should not >> attempt to ask for a reservation where start > end: >> >> >> memtype_reserve failed: [mem 0xffffffffff000-0x00008fff], req write-back >> >> The real question is which part of the call chain is responsible for >> this. That needs to be fixed. > > What about all the other ways in which a reservation request could be > invalid? The MM core already checks for these; what point is there in > duplicating these checks in many places higher up the call chain? Defensive programming rule #1: Check crap early but have the check which ultimatively catches it at the last possible place as well.