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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 EE22DC433E0 for ; Tue, 26 May 2020 07:20:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 87229207D8 for ; Tue, 26 May 2020 07:20:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="EjPwk0Na" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87229207D8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BFEFF80086; Tue, 26 May 2020 03:20:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BD87080061; Tue, 26 May 2020 03:20:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AC4FF80086; Tue, 26 May 2020 03:20:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0147.hostedemail.com [216.40.44.147]) by kanga.kvack.org (Postfix) with ESMTP id 9640B80061 for ; Tue, 26 May 2020 03:20:23 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 4825B181AC9BF for ; Tue, 26 May 2020 07:20:23 +0000 (UTC) X-FDA: 76858021926.23.crow00_5a6a47b679e63 X-HE-Tag: crow00_5a6a47b679e63 X-Filterd-Recvd-Size: 5371 Received: from mail27.static.mailgun.info (mail27.static.mailgun.info [104.130.122.27]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 26 May 2020 07:20:21 +0000 (UTC) DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1590477622; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=t71fVS7j/WcPCfl6939ZO5sEbx5ADmDSJSpSKaYbIN4=; b=EjPwk0NaTMXfcvojxeCtgMKNLALihd0ygc5mlorKcNlTtgFj296pslFRfVhLG0fL193+3fCP D2DPG8WrbW+lqHgNFp9afu8e3AnlSF5fCUp6GPf7jomoSWBKG7I2YHIk+mQeN5+gY1/jAEll 8sqg04/h2hXXjtvHIEIg8+GiHPg= X-Mailgun-Sending-Ip: 104.130.122.27 X-Mailgun-Sid: WyIwY2Q3OCIsICJsaW51eC1tbUBrdmFjay5vcmciLCAiYmU5ZTRhIl0= Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n02.prod.us-east-1.postgun.com with SMTP id 5eccc2ef2c5499847505408f (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 26 May 2020 07:19:11 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 58B1FC433CA; Tue, 26 May 2020 07:19:10 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: guptap) by smtp.codeaurora.org (Postfix) with ESMTPSA id B5261C433C6; Tue, 26 May 2020 07:19:09 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Date: Tue, 26 May 2020 12:49:09 +0530 From: guptap@codeaurora.org To: Robin Murphy Cc: Andrew Morton , mhocko@suse.com, joro@8bytes.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, owner-linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH] iommu/dma: limit iova free size to unmmaped iova In-Reply-To: <2d873ab9-ebb9-3c2d-f129-55a036ab47d0@arm.com> References: <20200521113004.12438-1-guptap@codeaurora.org> <7aaa8dcc-6a47-f256-431d-2a1b034b4076@arm.com> <90662ef3123dbf2e93f9718ee5cc14a7@codeaurora.org> <2d873ab9-ebb9-3c2d-f129-55a036ab47d0@arm.com> Message-ID: <4ba082d3bb965524157704ea1ffb1ff4@codeaurora.org> X-Sender: guptap@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 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 2020-05-22 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 making >> sure if unmap was successful should be sufficient before freeing iova.= =20 >> So change >> can instead be something like this: >>=20 >> -=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(cookie= , dma_addr, size); >>=20 >>> 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 first >>> place. >>>=20 >> 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 as= =20 >> valid >> iova and free. This part should be fixed. >=20 > 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. >=20 > 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. >=20 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 catch=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=20 BUG_ON(). Downgrading BUG_ON() to WARN_ON() in iova_magazine_free_pfns() will not=20 help much as invalid iova will cause NULL pointer dereference. 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=20 which eventually going to crash the system looks like iommu-dma layer issue. Thanks, Prakash