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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 E6429C433DF for ; Tue, 2 Jun 2020 13:07:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A4A5820674 for ; Tue, 2 Jun 2020 13:07:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A4A5820674 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 56B268E0006; Tue, 2 Jun 2020 09:07:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5198328007C; Tue, 2 Jun 2020 09:07:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 39ED88E0006; Tue, 2 Jun 2020 09:07:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0169.hostedemail.com [216.40.44.169]) by kanga.kvack.org (Postfix) with ESMTP id 23D0B8E0006 for ; Tue, 2 Jun 2020 09:07:33 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id D4D748248068 for ; Tue, 2 Jun 2020 13:07:32 +0000 (UTC) X-FDA: 76884298344.28.frogs06_226fc81d36957 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id 6A168A2DD; Tue, 2 Jun 2020 13:07:17 +0000 (UTC) X-HE-Tag: frogs06_226fc81d36957 X-Filterd-Recvd-Size: 5754 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf42.hostedemail.com (Postfix) with ESMTP; Tue, 2 Jun 2020 13:07:16 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A7A811FB; Tue, 2 Jun 2020 06:07:15 -0700 (PDT) Received: from [10.57.10.95] (unknown [10.57.10.95]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1BE473F305; Tue, 2 Jun 2020 06:07:13 -0700 (PDT) Subject: Re: [PATCH] iommu/dma: limit iova free size to unmmaped iova To: guptap@codeaurora.org Cc: mhocko@suse.com, owner-linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Andrew Morton References: <20200521113004.12438-1-guptap@codeaurora.org> <7aaa8dcc-6a47-f256-431d-2a1b034b4076@arm.com> <90662ef3123dbf2e93f9718ee5cc14a7@codeaurora.org> <2d873ab9-ebb9-3c2d-f129-55a036ab47d0@arm.com> <4ba082d3bb965524157704ea1ffb1ff4@codeaurora.org> From: Robin Murphy Message-ID: <9b5f8501-6e6e-0cd2-7f98-7cfea13051d7@arm.com> Date: Tue, 2 Jun 2020 14:07:12 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <4ba082d3bb965524157704ea1ffb1ff4@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB X-Rspamd-Queue-Id: 6A168A2DD X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 Content-Transfer-Encoding: quoted-printable 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 2020-05-26 08:19, guptap@codeaurora.org wrote: > On 2020-05-22 14:54, Robin Murphy wrote: >> On 2020-05-22 07:25, guptap@codeaurora.org wrote: >>> On 2020-05-22 01:46, Robin Murphy wrote: >>>> On 2020-05-21 12:30, Prakash Gupta wrote: >>> I agree, we shouldn't be freeing the partial iova. Instead just makin= g >>> sure if unmap was successful should be sufficient before freeing=20 >>> iova. So change >>> can instead be something like this: >>> >>> -=C2=A0=C2=A0=C2=A0 iommu_dma_free_iova(cookie, dma_addr, size); >>> +=C2=A0=C2=A0=C2=A0 if (unmapped) >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 iommu_dma_free_iova(cooki= e, dma_addr, size); >>> >>>> TBH my gut feeling here is that you're really just trying to treat a >>>> symptom of another bug elsewhere, namely some driver calling >>>> dma_unmap_* or dma_free_* with the wrong address or size in the firs= t >>>> place. >>>> >>> This condition would arise only if driver calling dma_unmap/free_*=20 >>> with 0 >>> iova_pfn. This will be flagged with a warning during unmap but will=20 >>> trigger >>> panic later on while doing unrelated dma_map/unmap_*. If unmapped has= =20 >>> already >>> failed for invalid iova, there is no reason we should consider this=20 >>> as valid >>> iova and free. This part should be fixed. >> >> I disagree. In general, if drivers call the DMA API incorrectly it is >> liable to lead to data loss, memory corruption, and various other >> unpleasant misbehaviour - it is not the DMA layer's job to attempt to >> paper over driver bugs. >> >> There *is* an argument for downgrading the BUG_ON() in >> iova_magazine_free_pfns() to a WARN_ON(), since frankly it isn't a >> sufficiently serious condition to justify killing the whole machine >> immediately, but NAK to bodging the iommu-dma mid-layer to "fix" that. >> A serious bug already happened elsewhere, so trying to hide the >> fallout really doesn't help anyone. >> > Sorry for delayed response, it was a long weekend. > I agree that invalid DMA API call can result in unexpected issues and=20 > client > should fix it, but then the present behavior makes it difficult to catc= h=20 > cases > when driver is making wrong DMA API calls. When invalid iova pfn is=20 > passed it > doesn't fail then and there, though DMA layer is aware of iova being=20 > invalid. It > fails much after that in the context of an valid map/unmap, with BUG_ON= (). >=20 > Downgrading BUG_ON() to WARN_ON() in iova_magazine_free_pfns() will not= =20 > help > much as invalid iova will cause NULL pointer dereference. Obviously I didn't mean a literal s/BUG/WARN/ substitution - some=20 additional control flow to actually handle the error case was implied. I'll write up the patch myself, since it's easier than further debating. > I see no reason why DMA layer wants to free an iova for which unmapped=20 > failed. > IMHO queuing an invalid iova (which already failed unmap) to rcache whi= ch > eventually going to crash the system looks like iommu-dma layer issue. What if the unmap fails because the address range is already entirely=20 unmapped? Freeing the IOVA (or at least attempting to) would be=20 logically appropriate in that case. In fact some IOMMU drivers might not=20 even consider that a failure, so the DMA layer may not even be aware=20 that it's been handed a bogus unallocated address. The point is that unmapping *doesn't* fail under normal and correct=20 operation, so the DMA layer should not expect to have to handle it. Even=20 if it does happen, that's a highly exceptional case that the DMA layer=20 cannot recover from by itself; at best it can just push the problem=20 elsewhere. It's pretty hard to justify doing extra work to simply move=20 an exceptional problem around without really addressing it. And in this particular case, personally I would *much* rather see=20 warnings spewing from both the pagetable and IOVA code as early as=20 possible to clearly indicate that the DMA layer itself has been thrown=20 out of sync, than just have warnings that might represent some other=20 source of pagetable corruption (or at worst, depending on the pagetable=20 code, no warnings at all and only have dma_map_*() calls quietly start=20 failing much, much later due to all the IOVA space having been leaked by=20 bad unmaps). Robin.