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 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 A0447C433E0 for ; Tue, 2 Jun 2020 09:39:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C65B207D5 for ; Tue, 2 Jun 2020 09:39:32 +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="mjglosZZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726759AbgFBJjb (ORCPT ); Tue, 2 Jun 2020 05:39:31 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:53635 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726110AbgFBJjb (ORCPT ); Tue, 2 Jun 2020 05:39:31 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1591090770; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=IekPtOjoRZDjZaNDXgKSitUXOmu6PIOrWvgVXoQjNic=; b=mjglosZZ7U2UYxX/BIM42Z21jV4QuJok2PWZNkpQ/0RW3mYthTpOKWUlbzuYxxTGyAmtHzry vYWQ2c+7VaVnTvvw8BEwjVOThQ6C3G/hhGV+aRbCxNdoEG5oqjIWOl7sqkyIzJWRsCgvCQ07 j/lW+Vn66KMRZSqIbQzCYXklJYo= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd 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-west-2.postgun.com with SMTP id 5ed61e5246d39fc0a2cc1a81 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 02 Jun 2020 09:39:30 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id EB705C433A0; Tue, 2 Jun 2020 09:39:29 +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 22DF2C433CA; Tue, 2 Jun 2020 09:39:29 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Tue, 02 Jun 2020 15:09:29 +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: <4ba082d3bb965524157704ea1ffb1ff4@codeaurora.org> 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> Message-ID: <2bfb4ce3a2dfeb2d585f0308a9002feb@codeaurora.org> X-Sender: guptap@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-26 12:49, 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 >>> making >>> sure if unmap was successful should be sufficient before freeing >>> iova. So change >>> can instead be something like this: >>> >>> -    iommu_dma_free_iova(cookie, dma_addr, size); >>> +    if (unmapped) >>> +        iommu_dma_free_iova(cookie, 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 >>>> first >>>> place. >>>> >>> This condition would arise only if driver calling dma_unmap/free_* >>> with 0 >>> iova_pfn. This will be flagged with a warning during unmap but will >>> trigger >>> panic later on while doing unrelated dma_map/unmap_*. If unmapped has >>> already >>> failed for invalid iova, there is no reason we should consider this >>> 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 > client > should fix it, but then the present behavior makes it difficult to > catch cases > when driver is making wrong DMA API calls. When invalid iova pfn is > passed it > doesn't fail then and there, though DMA layer is aware of iova being > invalid. It > fails much after that in the context of an valid map/unmap, with > BUG_ON(). > > Downgrading BUG_ON() to WARN_ON() in iova_magazine_free_pfns() will not > 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 > failed. > IMHO queuing an invalid iova (which already failed unmap) to rcache > which > eventually going to crash the system looks like iommu-dma layer issue. > > Thanks, > Prakash ping?