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Tue, 15 Sep 2020 14:11:54 +0000 Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 08FEBpVa026881; Tue, 15 Sep 2020 14:11:51 GMT Received: from [10.39.253.102] (/10.39.253.102) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 15 Sep 2020 14:11:50 +0000 Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference To: Christoph Hellwig References: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com> <20200915140719.GA14831@lst.de> From: Thomas Tai Message-ID: Date: Tue, 15 Sep 2020 10:11:51 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200915140719.GA14831@lst.de> Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9744 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 bulkscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 phishscore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150118 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9744 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 clxscore=1015 lowpriorityscore=0 phishscore=0 spamscore=0 priorityscore=1501 suspectscore=0 impostorscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150118 Cc: iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-kernel@vger.kernel.org, konrad.wilk@oracle.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2020-09-15 10:07 a.m., Christoph Hellwig wrote: > On Tue, Sep 15, 2020 at 08:03:14AM -0600, Thomas Tai wrote: >> When booting the kernel v5.9-rc4 on a VM, the kernel would panic when >> printing a warning message in swiotlb_map(). It is because dev->dma_mask >> can potentially be a null pointer. Using the dma_get_mask() macro can >> avoid the NULL pointer dereference. > > dma_mask must not be zero. This means drm is calling DMA API functions > on something weird. This needs to be fixed in the caller. > Thanks, Christoph for your comment. The caller already fixed the null pointer in the latest v5.9-rc5. I am thinking that if we had used the dma_get_mask(), the kernel couldn't panic and could properly print out the warning message. Thomas _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu