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, 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 9FDA2C433F5 for ; Mon, 13 Sep 2021 14:28:52 +0000 (UTC) Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) (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 400F960F58 for ; Mon, 13 Sep 2021 14:28:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 400F960F58 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=oss.oracle.com Received: from pps.filterd (m0246632.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.16.1.2/8.16.1.2) with SMTP id 18DEFe07027376; Mon, 13 Sep 2021 14:28:51 GMT Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by mx0b-00069f02.pphosted.com with ESMTP id 3b1k8sat6j-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 13 Sep 2021 14:28:50 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 18DEDPJk034901; Mon, 13 Sep 2021 14:28:49 GMT Received: from oss.oracle.com (oss-old-reserved.oracle.com [137.254.22.2]) by userp3020.oracle.com with ESMTP id 3b167qh6uk-1; Mon, 13 Sep 2021 14:28:49 +0000 Received: from localhost ([127.0.0.1] helo=lb-oss.oracle.com) by oss.oracle.com with esmtp (Exim 4.63) (envelope-from ) id 1mPmwy-0004d2-Jp; Mon, 13 Sep 2021 07:28:48 -0700 Received: from aserp3020.oracle.com ([141.146.126.70]) by oss.oracle.com with esmtp (Exim 4.63) (envelope-from ) id 1mK6AR-0001Av-0y for ocfs2-devel@oss.oracle.com; Sat, 28 Aug 2021 14:47:11 -0700 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 17SLfU3l082587 for ; Sat, 28 Aug 2021 21:47:10 GMT Received: from mx0a-00069f01.pphosted.com (mx0a-00069f01.pphosted.com [205.220.165.26]) by aserp3020.oracle.com with ESMTP id 3aqcy0pwnk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Sat, 28 Aug 2021 21:47:09 +0000 Received: from pps.filterd (m0246575.ppops.net [127.0.0.1]) by mx0b-00069f01.pphosted.com (8.16.1.2/8.16.0.43) with SMTP id 17SGfJdp029405 for ; Sat, 28 Aug 2021 21:47:08 GMT Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by mx0b-00069f01.pphosted.com with ESMTP id 3aqrvp1k3x-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO) for ; Sat, 28 Aug 2021 21:47:08 +0000 From: Thomas Gleixner To: "Luck, Tony" , Al Viro In-Reply-To: <20210827232246.GA1668365@agluck-desk2.amr.corp.intel.com> References: <20210827164926.1726765-1-agruenba@redhat.com> <20210827164926.1726765-6-agruenba@redhat.com> <20210827232246.GA1668365@agluck-desk2.amr.corp.intel.com> Date: Sat, 28 Aug 2021 23:47:03 +0200 Message-ID: <87r1edgs2w.ffs@tglx> MIME-Version: 1.0 X-Source-IP: 193.142.43.55 X-ServerName: galois.linutronix.de X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 mx -all X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10090 signatures=668682 X-Proofpoint-Spam-Details: rule=tap_notspam policy=tap score=0 mlxlogscore=614 impostorscore=0 lowpriorityscore=0 malwarescore=0 bulkscore=0 adultscore=0 phishscore=0 spamscore=0 clxscore=336 mlxscore=0 suspectscore=0 priorityscore=220 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108280152 X-Spam: Clean X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10090 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 phishscore=0 mlxscore=0 malwarescore=0 mlxlogscore=602 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108280151 X-Mailman-Approved-At: Mon, 13 Sep 2021 07:28:45 -0700 Cc: cluster-devel , Jan Kara , Andreas Gruenbacher , x86@kernel.org, Linux Kernel Mailing List , Christoph Hellwig , Borislav Petkov , linux-fsdevel , Linus Torvalds , ocfs2-devel@oss.oracle.com Subject: Re: [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable X-BeenThere: ocfs2-devel@oss.oracle.com X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: ocfs2-devel-bounces@oss.oracle.com Errors-To: ocfs2-devel-bounces@oss.oracle.com X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10105 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 adultscore=0 suspectscore=0 phishscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001 definitions=main-2109130095 X-Proofpoint-GUID: OTeV3d-5aBNVVmrXbFNBXE5HENAB0Fpg X-Proofpoint-ORIG-GUID: OTeV3d-5aBNVVmrXbFNBXE5HENAB0Fpg On Fri, Aug 27 2021 at 16:22, Tony Luck wrote: > On Fri, Aug 27, 2021 at 09:57:10PM +0000, Al Viro wrote: >> On Fri, Aug 27, 2021 at 09:48:55PM +0000, Al Viro wrote: >> >> > [btrfs]search_ioctl() >> > Broken with memory poisoning, for either variant of semantics. Same for >> > arm64 sub-page permission differences, I think. >> >> >> > So we have 3 callers where we want all-or-nothing semantics - two in >> > arch/x86/kernel/fpu/signal.c and one in btrfs. HWPOISON will be a problem >> > for all 3, AFAICS... >> > >> > IOW, it looks like we have two different things mixed here - one that wants >> > to try and fault stuff in, with callers caring only about having _something_ >> > faulted in (most of the users) and one that wants to make sure we *can* do >> > stores or loads on each byte in the affected area. >> > >> > Just accessing a byte in each page really won't suffice for the second kind. >> > Neither will g-u-p use, unless we teach it about HWPOISON and other fun >> > beasts... Looks like we want that thing to be a separate primitive; for >> > btrfs I'd probably replace fault_in_pages_writeable() with clear_user() >> > as a quick fix for now... >> > >> > Comments? >> >> Wait a sec... Wasn't HWPOISON a per-page thing? arm64 definitely does have >> smaller-than-page areas with different permissions, so btrfs search_ioctl() >> has a problem there, but arch/x86/kernel/fpu/signal.c doesn't have to deal >> with that... >> >> Sigh... I really need more coffee... > > On Intel poison is tracked at the cache line granularity. Linux > inflates that to per-page (because it can only take a whole page away). > For faults triggered in ring3 this is pretty much the same thing because > mm/memory_failure.c unmaps the page ... so while you see a #MC on first > access, you get #PF when you retry. The x86 fault handler sees a magic > signature in the page table and sends a SIGBUS. > > But it's all different if the #MC is triggerd from ring0. The machine > check handler can't unmap the page. It just schedules task_work to do > the unmap when next returning to the user. > > But if your kernel code loops and tries again without a return to user, > then your get another #MC. But that's not the case for restore_fpregs_from_user() when it hits #MC. restore_fpregs_from_user() ... ret = __restore_fpregs_from_user(buf, xrestore, fx_only) /* Try to handle #PF, but anything else is fatal. */ if (ret != -EFAULT) return -EINVAL; Now let's look at __restore_fpregs_from_user() __restore_fpregs_from_user() return $FPUVARIANT_rstor_from_user_sigframe() which all end up in user_insn(). user_insn() returns 0 or the negated trap number, which results in -EFAULT for #PF, but for #MC the negated trap number is -18 i.e. != -EFAULT. IOW, there is no endless loop. This used to be a problem before commit: aee8c67a4faa ("x86/fpu: Return proper error codes from user access functions") and as the changelog says the initial reason for this was #GP going into the fault path, but I'm pretty sure that I also discussed the #MC angle with Borislav back then. Should have added some more comments there obviously. Thanks, tglx _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel