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Mon, 17 Aug 2020 18:30:56 +0000 Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 07HIUrEr019206; Mon, 17 Aug 2020 18:30:54 GMT Received: from [10.39.206.110] (/10.39.206.110) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 17 Aug 2020 11:30:53 -0700 Subject: Re: [PATCH V1 18/32] osdep: import MADV_DOEXEC To: qemu-devel@nongnu.org, Alex Williamson References: <1596122076-341293-1-git-send-email-steven.sistare@oracle.com> <1596122076-341293-19-git-send-email-steven.sistare@oracle.com> From: Steven Sistare Organization: Oracle Corporation Message-ID: <51c859fb-3340-e361-1945-0ec2a393a34d@oracle.com> Date: Mon, 17 Aug 2020 14:30:51 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <1596122076-341293-19-git-send-email-steven.sistare@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9716 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 malwarescore=0 mlxscore=0 phishscore=0 spamscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008170129 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9716 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 impostorscore=0 mlxlogscore=999 priorityscore=1501 phishscore=0 spamscore=0 mlxscore=0 adultscore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008170129 Received-SPF: pass client-ip=156.151.31.86; envelope-from=steven.sistare@oracle.com; helo=userp2130.oracle.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/17 14:31:01 X-ACL-Warn: Detected OS = Linux 3.1-3.10 [fuzzy] X-Spam_score_int: -63 X-Spam_score: -6.4 X-Spam_bar: ------ X-Spam_report: (-6.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P. Berrange" , "Michael S. Tsirkin" , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Juan Quintela , "Dr. David Alan Gilbert" , Markus Armbruster , Stefan Hajnoczi , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/30/2020 11:14 AM, Steve Sistare wrote: > Anonymous memory segments used by the guest are preserved across a re-exec > of qemu, mapped at the same VA, via a proposed madvise(MADV_DOEXEC) option > in the Linux kernel. For the madvise patches, see: > > https://lore.kernel.org/lkml/1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com/ > > Signed-off-by: Steve Sistare > --- > include/qemu/osdep.h | 7 +++++++ > 1 file changed, 7 insertions(+) Hi Alex, The MADV_DOEXEC functionality, which is a pre-requisite for the entire qemu live update series, is getting a chilly reception on lkml. We could instead create guest memory using memfd_create and preserve the fd across exec. However, the subsequent mmap(fd) will return a different VA than was used previously, which is a problem for memory that was registered with vfio, as the original VA is remembered in the kernel struct vfio_dma and used in various kernel functions, such as vfio_iommu_replay. To fix, we could provide a VFIO_IOMMU_REMAP_DMA ioctl taking iova, size, and new_vaddr. The implementation finds an exact match for (iova, size) and replaces vaddr with new_vaddr. Flags cannot be changed. memfd_create plus VFIO_IOMMU_REMAP_DMA would replace MADV_DOEXEC. vfio on any form of shared memory (shm, dax, etc) could also be preserved across exec with shmat/mmap plus VFIO_IOMMU_REMAP_DMA. What do you think? - Steve