This series enable shadow virtqueue (SVQ) for vhost-vdpa devices. This is intended as a new method of tracking the memory the devices touch during a migration process: Instead of relay on vhost device's dirty logging capability, SVQ intercepts the VQ dataplane forwarding the descriptors between VM and device. This way qemu is the effective writer of guests memory, like in qemu's virtio device operation.
When SVQ is enabled qemu offers a new virtual address space to the device to read and write into, and it maps new vrings and the guest memory in it. SVQ also intercepts kicks and calls between the device and the guest. Used buffers relay would cause dirty memory being tracked. This effectively means that vDPA device passthrough is intercepted by qemu. While SVQ should only be enabled at migration time, the switching from regular mode to SVQ mode is left for a future series. It is based on the ideas of DPDK SW assisted LM, in the series of DPDK's https://patchwork.dpdk.org/cover/48370/ . However, these does not map the shadow vq in guest's VA, but in qemu's. For qemu to use shadow virtqueues the guest virtio driver must not use features like event_idx, indirect descriptors, packed and in_order. These features are easy to implement on top of this base, but is left for a future series for simplicity. SVQ needs to be enabled at qemu start time with vdpa cmdline parameter: -netdev type=vhost-vdpa,vhostdev=vhost-vdpa-0,id=vhost-vdpa0,x-svq=off The first three patches enables notifications forwarding with assistance of qemu. It's easy to enable only this if the relevant cmdline part of the last patch is applied on top of these. Next four patches implement the actual buffer forwarding. However, address are not translated from HVA so they will need a host device with an iommu allowing them to access all of the HVA range. The last part of the series uses properly the host iommu, so qemu creates a new iova address space in the device's range and translates the buffers in it. Finally, it adds the cmdline parameter. Some simple performance tests with netperf were done. They used a nested guest with vp_vdpa, vhost-kernel at L0 host. Starting with no svq and a baseline average of ~9980.13Mbps: Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 131072 16384 16384 30.01 9910.61 131072 16384 16384 30.00 10030.94 131072 16384 16384 30.01 9998.84 To enable the notifications interception reduced performance to an average of ~9577.73Mbit/s: Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 131072 16384 16384 30.00 9563.03 131072 16384 16384 30.01 9626.65 131072 16384 16384 30.01 9543.51 Finally, to enable buffers forwarding reduced the throughput again to ~8902.92Mbit/s: Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 131072 16384 16384 30.01 8643.19 131072 16384 16384 30.01 9033.56 131072 16384 16384 30.01 9032.02 However, many performance improvements were left out of this series for simplicity, so difference if performance should shrink in the future. Comments are welcome. TODO in future series: * Event, indirect, packed, and others features of virtio. * To support different set of features between the device<->SVQ and the SVQ<->guest communication. * Support of device host notifier memory regions. * To sepparate buffers forwarding in its own AIO context, so we can throw more threads to that task and we don't need to stop the main event loop. * Support multiqueue virtio-net vdpa. * Proper documentation. Changes from v1: * Feature set at device->SVQ is now the same as SVQ->guest. * Size of SVQ is not max available device size anymore, but guest's negotiated. * Add VHOST_FILE_UNBIND kick and call fd treatment. * Make SVQ a public struct * Come back to previous approach to iova-tree * Some assertions are now fail paths. Some errors are now log_guest. * Only mask _F_LOG feature at vdpa_set_features svq enable path. * Refactor some errors and messages. Add missing error unwindings. * Add memory barrier at _F_NO_NOTIFY set. * Stop checking for features flags out of transport range. v1 link: https://lore.kernel.org/virtualization/7d86c715-6d71-8a27-91f5-8d47b71e3...@redhat.com/ Changes from v4 RFC: * Support of allocating / freeing iova ranges in IOVA tree. Extending already present iova-tree for that. * Proper validation of guest features. Now SVQ can negotiate a different set of features with the device when enabled. * Support of host notifiers memory regions * Handling of SVQ full queue in case guest's descriptors span to different memory regions (qemu's VA chunks). * Flush pending used buffers at end of SVQ operation. * QMP command now looks by NetClientState name. Other devices will need to implement it's way to enable vdpa. * Rename QMP command to set, so it looks more like a way of working * Better use of qemu error system * Make a few assertions proper error-handling paths. * Add more documentation * Less coupling of virtio / vhost, that could cause friction on changes * Addressed many other small comments and small fixes. Changes from v3 RFC: * Move everything to vhost-vdpa backend. A big change, this allowed some cleanup but more code has been added in other places. * More use of glib utilities, especially to manage memory. v3 link: https://lists.nongnu.org/archive/html/qemu-devel/2021-05/msg06032.html Changes from v2 RFC: * Adding vhost-vdpa devices support * Fixed some memory leaks pointed by different comments v2 link: https://lists.nongnu.org/archive/html/qemu-devel/2021-03/msg05600.html Changes from v1 RFC: * Use QMP instead of migration to start SVQ mode. * Only accepting IOMMU devices, closer behavior with target devices (vDPA) * Fix invalid masking/unmasking of vhost call fd. * Use of proper methods for synchronization. * No need to modify VirtIO device code, all of the changes are contained in vhost code. * Delete superfluous code. * An intermediate RFC was sent with only the notifications forwarding changes. It can be seen in https://patchew.org/QEMU/20210129205415.876290-1-epere...@redhat.com/ v1 link: https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05372.html Eugenio Pérez (20): virtio: Add VIRTIO_F_QUEUE_STATE virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED virtio: Add virtio_queue_is_host_notifier_enabled vhost: Make vhost_virtqueue_{start,stop} public vhost: Add x-vhost-enable-shadow-vq qmp vhost: Add VhostShadowVirtqueue vdpa: Register vdpa devices in a list vhost: Route guest->host notification through shadow virtqueue Add vhost_svq_get_svq_call_notifier Add vhost_svq_set_guest_call_notifier vdpa: Save call_fd in vhost-vdpa vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call vhost: Route host->guest notification through shadow virtqueue virtio: Add vhost_shadow_vq_get_vring_addr vdpa: Save host and guest features vhost: Add vhost_svq_valid_device_features to shadow vq vhost: Shadow virtqueue buffers forwarding vhost: Add VhostIOVATree vhost: Use a tree to store memory mappings vdpa: Add custom IOTLB translations to SVQ Eugenio Pérez (14): vhost: Add VhostShadowVirtqueue vhost: Add Shadow VirtQueue kick forwarding capabilities vhost: Add Shadow VirtQueue call forwarding capabilities vhost: Add vhost_svq_valid_features to shadow vq virtio: Add vhost_shadow_vq_get_vring_addr vdpa: adapt vhost_ops callbacks to svq vhost: Shadow virtqueue buffers forwarding util: Add iova_tree_alloc vhost: Add VhostIOVATree vdpa: Add custom IOTLB translations to SVQ vdpa: Adapt vhost_vdpa_get_vring_base to SVQ vdpa: Never set log_base addr if SVQ is enabled vdpa: Expose VHOST_F_LOG_ALL on SVQ vdpa: Add x-svq to NetdevVhostVDPAOptions qapi/net.json | 5 +- hw/virtio/vhost-iova-tree.h | 27 ++ hw/virtio/vhost-shadow-virtqueue.h | 90 ++++ include/hw/virtio/vhost-vdpa.h | 8 + include/qemu/iova-tree.h | 18 + hw/virtio/vhost-iova-tree.c | 155 +++++++ hw/virtio/vhost-shadow-virtqueue.c | 632 +++++++++++++++++++++++++++++ hw/virtio/vhost-vdpa.c | 551 ++++++++++++++++++++++++- net/vhost-vdpa.c | 48 ++- util/iova-tree.c | 133 ++++++ hw/virtio/meson.build | 2 +- 11 files changed, 1644 insertions(+), 25 deletions(-) create mode 100644 hw/virtio/vhost-iova-tree.h create mode 100644 hw/virtio/vhost-shadow-virtqueue.h create mode 100644 hw/virtio/vhost-iova-tree.c create mode 100644 hw/virtio/vhost-shadow-virtqueue.c -- 2.27.0