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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 A3BE5C7618B for ; Tue, 23 Jul 2019 15:47:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7EA10218D3 for ; Tue, 23 Jul 2019 15:47:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731338AbfGWPrf (ORCPT ); Tue, 23 Jul 2019 11:47:35 -0400 Received: from mail-ua1-f65.google.com ([209.85.222.65]:39680 "EHLO mail-ua1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726347AbfGWPrf (ORCPT ); Tue, 23 Jul 2019 11:47:35 -0400 Received: by mail-ua1-f65.google.com with SMTP id j8so17075072uan.6 for ; Tue, 23 Jul 2019 08:47:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=EVAD8Vf0X0incVqfNJDqjZVDQjwtcJn0P5gsd+3TH3w=; b=Tvd16/uMoLKLGq1S66bHVGyTAF+u81/kWgrZJuFvEQb75Yl04clJoziU+7EwQf1fsg f8G7GsEL0qeIimikfwEKama/v8nnJf8cWaqLwan6fksUsIgSln4RelzOpJyrT8hBZD/y cfWOt2c1dVVIF6DCO+RhQrfm7yoqVJflmWg1k6DituW6/sq0Og/uwZYzZWQwZzrgnqT2 aZuBYzsrYFaS0tyPjZ79zOJbnSUsghpDFt8w5mKkvh7wLhWr2knlEjw/k6EFMKv48SsH EF3qbFYSwYFGgVTDt6YhiH6Spv1zvOS+VLsT+7HywlPuYXhXZwFd5Ut41aPCEfOSKFag nurQ== X-Gm-Message-State: APjAAAVDfuToNaFHBGJrBjBuJQa7qmhqRUQTWVJmpQ4iB6SZXNed6uDu sF7uMjJvdOkQz/4w8Ig7g3qbQw== X-Google-Smtp-Source: APXvYqzIzHEVdbHcpvt3jUNOAipVxZHK2T6eMul3vNE3BHOosQ4+ZcwjKuMyZs2L9p2YrV6mjmClLw== X-Received: by 2002:ab0:734f:: with SMTP id k15mr19186395uap.28.1563896853769; Tue, 23 Jul 2019 08:47:33 -0700 (PDT) Received: from redhat.com (bzq-79-181-91-42.red.bezeqint.net. [79.181.91.42]) by smtp.gmail.com with ESMTPSA id j138sm17625220vka.11.2019.07.23.08.47.29 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Jul 2019 08:47:32 -0700 (PDT) Date: Tue, 23 Jul 2019 11:47:27 -0400 From: "Michael S. Tsirkin" To: Christoph Hellwig Cc: Eric Auger , eric.auger.pro@gmail.com, m.szyprowski@samsung.com, robin.murphy@arm.com, jasowang@redhat.com, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call Message-ID: <20190723114504-mutt-send-email-mst@kernel.org> References: <20190722145509.1284-1-eric.auger@redhat.com> <20190722145509.1284-3-eric.auger@redhat.com> <20190722112704-mutt-send-email-mst@kernel.org> <20190723153830.GD720@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190723153830.GD720@lst.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 23, 2019 at 05:38:30PM +0200, Christoph Hellwig wrote: > On Mon, Jul 22, 2019 at 11:33:35AM -0400, Michael S. Tsirkin wrote: > > On Mon, Jul 22, 2019 at 04:55:09PM +0200, Eric Auger wrote: > > > Do not call dma_max_mapping_size for devices that have no DMA > > > mask set, otherwise we can hit a NULL pointer dereference. > > > > > > This occurs when a virtio-blk-pci device is protected with > > > a virtual IOMMU. > > > > > > Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()") > > > Signed-off-by: Eric Auger > > > Suggested-by: Christoph Hellwig > > > > Christoph, I wonder why did you suggest this? > > The connection between dma_mask and dma_max_mapping_size > > is far from obvious. The documentation doesn't exist. > > Do we really have to teach all users about this hack? > > Why not just make dma_max_mapping_size DTRT? > > Because we should not call into dma API functions for devices that > are not DMA capable. I'd rather call is_device_dma_capable then, better than poking at DMA internals. -- MST