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[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 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-Disposition: inline In-Reply-To: <20190723153830.GD720@lst.de> Cc: jasowang@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, eric.auger.pro@gmail.com, robin.murphy@arm.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu