From: Alex Williamson <alex.williamson@redhat.com> To: Jason Gunthorpe <jgg@nvidia.com> Cc: Yi Liu <yi.l.liu@intel.com>, "Tian, Kevin" <kevin.tian@intel.com>, "Peng, Chao P" <chao.p.peng@intel.com>, "Sun, Yi Y" <yi.y.sun@intel.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>, "thuth@redhat.com" <thuth@redhat.com>, "farman@linux.ibm.com" <farman@linux.ibm.com>, "mjrosato@linux.ibm.com" <mjrosato@linux.ibm.com>, "akrowiak@linux.ibm.com" <akrowiak@linux.ibm.com>, "pasic@linux.ibm.com" <pasic@linux.ibm.com>, "jjherne@linux.ibm.com" <jjherne@linux.ibm.com>, "jasowang@redhat.com" <jasowang@redhat.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "nicolinc@nvidia.com" <nicolinc@nvidia.com>, "eric.auger@redhat.com" <eric.auger@redhat.com>, "eric.auger.pro@gmail.com" <eric.auger.pro@gmail.com>, "peterx@redhat.com" <peterx@redhat.com> Subject: Re: [RFC 15/18] vfio/iommufd: Implement iommufd backend Date: Tue, 26 Apr 2022 12:45:41 -0600 [thread overview] Message-ID: <20220426124541.5f33f357.alex.williamson@redhat.com> (raw) In-Reply-To: <20220426141156.GO2125828@nvidia.com> On Tue, 26 Apr 2022 11:11:56 -0300 Jason Gunthorpe <jgg@nvidia.com> wrote: > On Tue, Apr 26, 2022 at 10:08:30PM +0800, Yi Liu wrote: > > > > I think it is strange that the allowed DMA a guest can do depends on > > > the order how devices are plugged into the guest, and varys from > > > device to device? > > > > > > IMHO it would be nicer if qemu would be able to read the new reserved > > > regions and unmap the conflicts before hot plugging the new device. We > > > don't have a kernel API to do this, maybe we should have one? > > > > For userspace drivers, it is fine to do it. For QEMU, it's not quite easy > > since the IOVA is GPA which is determined per the e820 table. > > Sure, that is why I said we may need a new API to get this data back > so userspace can fix the address map before attempting to attach the > new device. Currently that is not possible at all, the device attach > fails and userspace has no way to learn what addresses are causing > problems. We have APIs to get the IOVA ranges, both with legacy vfio and the iommufd RFC, QEMU could compare these, but deciding to remove an existing mapping is not something to be done lightly. We must be absolutely certain that there is no DMA to that range before doing so. > > > eg currently I see the log messages that it is passing P2P BAR memory > > > into iommufd map, this should be prevented inside qemu because it is > > > not reliable right now if iommufd will correctly reject it. > > > > yeah. qemu can filter the P2P BAR mapping and just stop it in qemu. We > > haven't added it as it is something you will add in future. so didn't > > add it in this RFC. :-) Please let me know if it feels better to filter > > it from today. > > I currently hope it will use a different map API entirely and not rely > on discovering the P2P via the VMA. eg using a DMABUF FD or something. > > So blocking it in qemu feels like the right thing to do. Wait a sec, so legacy vfio supports p2p between devices, which has a least a couple known use cases, primarily involving GPUs for at least one of the peers, and we're not going to make equivalent support a feature requirement for iommufd? This would entirely fracture the notion that iommufd is a direct replacement and upgrade from legacy vfio and make a transparent transition for libvirt managed VMs impossible. Let's reconsider. Thanks, Alex
WARNING: multiple messages have this Message-ID (diff)
From: Alex Williamson <alex.williamson@redhat.com> To: Jason Gunthorpe <jgg@nvidia.com> Cc: "akrowiak@linux.ibm.com" <akrowiak@linux.ibm.com>, "jjherne@linux.ibm.com" <jjherne@linux.ibm.com>, "Tian, Kevin" <kevin.tian@intel.com>, "Peng, Chao P" <chao.p.peng@intel.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "mjrosato@linux.ibm.com" <mjrosato@linux.ibm.com>, "farman@linux.ibm.com" <farman@linux.ibm.com>, "jasowang@redhat.com" <jasowang@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "peterx@redhat.com" <peterx@redhat.com>, "pasic@linux.ibm.com" <pasic@linux.ibm.com>, "eric.auger@redhat.com" <eric.auger@redhat.com>, "Sun, Yi Y" <yi.y.sun@intel.com>, Yi Liu <yi.l.liu@intel.com>, "nicolinc@nvidia.com" <nicolinc@nvidia.com>, "thuth@redhat.com" <thuth@redhat.com>, "eric.auger.pro@gmail.com" <eric.auger.pro@gmail.com>, "david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au> Subject: Re: [RFC 15/18] vfio/iommufd: Implement iommufd backend Date: Tue, 26 Apr 2022 12:45:41 -0600 [thread overview] Message-ID: <20220426124541.5f33f357.alex.williamson@redhat.com> (raw) In-Reply-To: <20220426141156.GO2125828@nvidia.com> On Tue, 26 Apr 2022 11:11:56 -0300 Jason Gunthorpe <jgg@nvidia.com> wrote: > On Tue, Apr 26, 2022 at 10:08:30PM +0800, Yi Liu wrote: > > > > I think it is strange that the allowed DMA a guest can do depends on > > > the order how devices are plugged into the guest, and varys from > > > device to device? > > > > > > IMHO it would be nicer if qemu would be able to read the new reserved > > > regions and unmap the conflicts before hot plugging the new device. We > > > don't have a kernel API to do this, maybe we should have one? > > > > For userspace drivers, it is fine to do it. For QEMU, it's not quite easy > > since the IOVA is GPA which is determined per the e820 table. > > Sure, that is why I said we may need a new API to get this data back > so userspace can fix the address map before attempting to attach the > new device. Currently that is not possible at all, the device attach > fails and userspace has no way to learn what addresses are causing > problems. We have APIs to get the IOVA ranges, both with legacy vfio and the iommufd RFC, QEMU could compare these, but deciding to remove an existing mapping is not something to be done lightly. We must be absolutely certain that there is no DMA to that range before doing so. > > > eg currently I see the log messages that it is passing P2P BAR memory > > > into iommufd map, this should be prevented inside qemu because it is > > > not reliable right now if iommufd will correctly reject it. > > > > yeah. qemu can filter the P2P BAR mapping and just stop it in qemu. We > > haven't added it as it is something you will add in future. so didn't > > add it in this RFC. :-) Please let me know if it feels better to filter > > it from today. > > I currently hope it will use a different map API entirely and not rely > on discovering the P2P via the VMA. eg using a DMABUF FD or something. > > So blocking it in qemu feels like the right thing to do. Wait a sec, so legacy vfio supports p2p between devices, which has a least a couple known use cases, primarily involving GPUs for at least one of the peers, and we're not going to make equivalent support a feature requirement for iommufd? This would entirely fracture the notion that iommufd is a direct replacement and upgrade from legacy vfio and make a transparent transition for libvirt managed VMs impossible. Let's reconsider. Thanks, Alex
next prev parent reply other threads:[~2022-04-26 18:45 UTC|newest] Thread overview: 125+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-14 10:46 [RFC 00/18] vfio: Adopt iommufd Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 01/18] scripts/update-linux-headers: Add iommufd.h Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 02/18] linux-headers: Import latest vfio.h and iommufd.h Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 03/18] hw/vfio/pci: fix vfio_pci_hot_reset_result trace point Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 04/18] vfio/pci: Use vbasedev local variable in vfio_realize() Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 05/18] vfio/common: Rename VFIOGuestIOMMU::iommu into ::iommu_mr Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-14 10:46 ` [RFC 06/18] vfio/common: Split common.c into common.c, container.c and as.c Yi Liu 2022-04-14 10:46 ` [RFC 07/18] vfio: Add base object for VFIOContainer Yi Liu 2022-04-14 10:46 ` Yi Liu 2022-04-29 6:29 ` David Gibson 2022-04-29 6:29 ` David Gibson 2022-05-03 13:05 ` Yi Liu 2022-04-14 10:47 ` [RFC 08/18] vfio/container: Introduce vfio_[attach/detach]_device Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 09/18] vfio/platform: Use vfio_[attach/detach]_device Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 10/18] vfio/ap: " Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 11/18] vfio/ccw: " Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 12/18] vfio/container-obj: Introduce [attach/detach]_device container callbacks Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 13/18] vfio/container-obj: Introduce VFIOContainer reset callback Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 14/18] hw/iommufd: Creation Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 15/18] vfio/iommufd: Implement iommufd backend Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-22 14:58 ` Jason Gunthorpe 2022-04-22 21:33 ` Alex Williamson 2022-04-22 21:33 ` Alex Williamson 2022-04-26 9:55 ` Yi Liu 2022-04-26 9:55 ` Yi Liu 2022-04-26 10:41 ` Tian, Kevin 2022-04-26 10:41 ` Tian, Kevin 2022-04-26 13:41 ` Jason Gunthorpe 2022-04-26 14:08 ` Yi Liu 2022-04-26 14:08 ` Yi Liu 2022-04-26 14:11 ` Jason Gunthorpe 2022-04-26 18:45 ` Alex Williamson [this message] 2022-04-26 18:45 ` Alex Williamson 2022-04-26 19:27 ` Jason Gunthorpe 2022-04-26 20:59 ` Alex Williamson 2022-04-26 20:59 ` Alex Williamson 2022-04-26 23:08 ` Jason Gunthorpe 2022-04-26 13:53 ` Jason Gunthorpe 2022-04-14 10:47 ` [RFC 16/18] vfio/iommufd: Add IOAS_COPY_DMA support Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 17/18] vfio/as: Allow the selection of a given iommu backend Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-14 10:47 ` [RFC 18/18] vfio/pci: Add an iommufd option Yi Liu 2022-04-14 10:47 ` Yi Liu 2022-04-15 8:37 ` [RFC 00/18] vfio: Adopt iommufd Nicolin Chen 2022-04-17 10:30 ` Eric Auger 2022-04-17 10:30 ` Eric Auger 2022-04-19 3:26 ` Nicolin Chen 2022-04-25 19:40 ` Eric Auger 2022-04-25 19:40 ` Eric Auger 2022-04-18 8:49 ` Tian, Kevin 2022-04-18 8:49 ` Tian, Kevin 2022-04-18 12:09 ` Yi Liu 2022-04-18 12:09 ` Yi Liu 2022-04-25 19:51 ` Eric Auger 2022-04-25 19:51 ` Eric Auger 2022-04-25 19:55 ` Eric Auger 2022-04-25 19:55 ` Eric Auger 2022-04-26 8:39 ` Tian, Kevin 2022-04-26 8:39 ` Tian, Kevin 2022-04-22 22:09 ` Alex Williamson 2022-04-22 22:09 ` Alex Williamson 2022-04-25 10:10 ` Daniel P. Berrangé 2022-04-25 10:10 ` Daniel P. Berrangé 2022-04-25 13:36 ` Jason Gunthorpe 2022-04-25 14:37 ` Alex Williamson 2022-04-25 14:37 ` Alex Williamson 2022-04-26 8:37 ` Tian, Kevin 2022-04-26 8:37 ` Tian, Kevin 2022-04-26 12:33 ` Jason Gunthorpe 2022-04-26 16:21 ` Alex Williamson 2022-04-26 16:21 ` Alex Williamson 2022-04-26 16:42 ` Jason Gunthorpe 2022-04-26 19:24 ` Alex Williamson 2022-04-26 19:24 ` Alex Williamson 2022-04-26 19:36 ` Jason Gunthorpe 2022-04-28 3:21 ` Tian, Kevin 2022-04-28 3:21 ` Tian, Kevin 2022-04-28 14:24 ` Alex Williamson 2022-04-28 14:24 ` Alex Williamson 2022-04-28 16:20 ` Daniel P. Berrangé 2022-04-28 16:20 ` Daniel P. Berrangé 2022-04-29 0:45 ` Tian, Kevin 2022-04-29 0:45 ` Tian, Kevin 2022-04-25 20:23 ` Eric Auger 2022-04-25 20:23 ` Eric Auger 2022-04-25 22:53 ` Alex Williamson 2022-04-25 22:53 ` Alex Williamson 2022-04-26 9:47 ` Shameerali Kolothum Thodi via 2022-04-26 9:47 ` Shameerali Kolothum Thodi 2022-04-26 11:44 ` Eric Auger 2022-04-26 11:44 ` Eric Auger 2022-04-26 12:43 ` Shameerali Kolothum Thodi 2022-04-26 12:43 ` Shameerali Kolothum Thodi via 2022-04-26 16:35 ` Alex Williamson 2022-04-26 16:35 ` Alex Williamson 2022-05-09 14:24 ` Zhangfei Gao 2022-05-10 3:17 ` Yi Liu 2022-05-10 6:51 ` Eric Auger 2022-05-10 12:35 ` Zhangfei Gao 2022-05-10 12:45 ` Jason Gunthorpe 2022-05-10 14:08 ` Yi Liu 2022-05-11 14:17 ` zhangfei.gao 2022-05-12 9:01 ` zhangfei.gao 2022-05-17 8:55 ` Yi Liu 2022-05-18 7:22 ` zhangfei.gao 2022-05-18 14:00 ` Yi Liu 2022-06-28 8:14 ` Shameerali Kolothum Thodi 2022-06-28 8:14 ` Shameerali Kolothum Thodi via 2022-06-28 8:58 ` Eric Auger 2022-05-17 8:52 ` Yi Liu
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