? 2022/1/22 ??4:27, Eugenio P?rez ??:> This series enables 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 emulated 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, but at this RFC SVQ is not enabled on migration automatically.
>
> Thanks of being a buffers relay system, SVQ can be used also to
> communicate devices and drivers with different capabilities, like
> devices that only support packed vring and not split and old guests with
> no driver packed support.
>
> 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.
>
> This version of SVQ is limited in the amount of features it can use with
> guest and device, because this series is already very big otherwise.
> Features like indirect or event_idx will be addressed in future series.
>
> SVQ needs to be enabled with cmdline parameter x-svq, like:
>
> -netdev
type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=true
>
> In this version it cannot be enabled or disabled in runtime. Further
> series will remove this limitation and will enable it only for migration
> time.
>
> Some patches are intentionally very small to ease review, but they can
> be squashed if preferred.
>
> Patches 1-10 prepares the SVQ and QEMU to support both guest to device
> and device to guest notifications forwarding, with the extra qemu hop.
> That part can be tested in isolation if cmdline change is reproduced.
>
> Patches from 11 to 18 implement the actual buffer forwarding, but with
> no IOMMU support. It requires a vdpa device capable of addressing all
> qemu vaddr.
>
> Patches 19 to 23 adds the iommu support, so the device with address
> range limitations can access SVQ through this new virtual address space
> created.
>
> The rest of the series add the last pieces needed for migration.
>
> Comments are welcome.
I wonder the performance impact. So performance numbers are more than
welcomed.
Thanks
>
> TODO:
> * Event, indirect, packed, and other features of virtio.
> * To separate 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 virtio-net control vq.
> * Proper documentation.
>
> Changes from v5 RFC:
> * Remove dynamic enablement of SVQ, making less dependent of the device.
> * Enable live migration if SVQ is enabled.
> * Fix SVQ when driver reset.
> * Comments addressed, specially in the iova area.
> * Rebase on latest master, adding multiqueue support (but no networking
> control vq processing).
> v5 link:
> https://lists.gnu.org/archive/html/qemu-devel/2021-10/msg07250.html
>
> 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-eperezma at
redhat.com/
> v1 link:
> https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05372.html
>
> Eugenio P?rez (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 P?rez (31):
> vdpa: Reorder virtio/vhost-vdpa.c functions
> vhost: Add VhostShadowVirtqueue
> vdpa: Add vhost_svq_get_dev_kick_notifier
> vdpa: Add vhost_svq_set_svq_kick_fd
> vhost: Add Shadow VirtQueue kick forwarding capabilities
> vhost: Route guest->host notification through shadow virtqueue
> vhost: dd vhost_svq_get_svq_call_notifier
> vhost: Add vhost_svq_set_guest_call_notifier
> vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call
> vhost: Route host->guest notification through shadow virtqueue
> vhost: Add vhost_svq_valid_device_features to shadow vq
> vhost: Add vhost_svq_valid_guest_features to shadow vq
> vhost: Add vhost_svq_ack_guest_features to shadow vq
> virtio: Add vhost_shadow_vq_get_vring_addr
> vdpa: Add vhost_svq_get_num
> vhost: pass queue index to vhost_vq_get_addr
> vdpa: adapt vhost_ops callbacks to svq
> vhost: Shadow virtqueue buffers forwarding
> utils: Add internal DMAMap to iova-tree
> util: Store DMA entries in a list
> util: Add iova_tree_alloc
> vhost: Add VhostIOVATree
> vdpa: Add custom IOTLB translations to SVQ
> vhost: Add vhost_svq_get_last_used_idx
> vdpa: Adapt vhost_vdpa_get_vring_base to SVQ
> vdpa: Clear VHOST_VRING_F_LOG at vhost_vdpa_set_vring_addr in SVQ
> vdpa: Never set log_base addr if SVQ is enabled
> vdpa: Expose VHOST_F_LOG_ALL on SVQ
> vdpa: Make ncs autofree
> vdpa: Move vhost_vdpa_get_iova_range to net/vhost-vdpa.c
> vdpa: Add x-svq to NetdevVhostVDPAOptions
>
> qapi/net.json | 5 +-
> hw/virtio/vhost-iova-tree.h | 27 +
> hw/virtio/vhost-shadow-virtqueue.h | 46 ++
> include/hw/virtio/vhost-vdpa.h | 7 +
> include/qemu/iova-tree.h | 17 +
> hw/virtio/vhost-iova-tree.c | 157 ++++++
> hw/virtio/vhost-shadow-virtqueue.c | 761 +++++++++++++++++++++++++++++
> hw/virtio/vhost-vdpa.c | 740 ++++++++++++++++++++++++----
> hw/virtio/vhost.c | 6 +-
> net/vhost-vdpa.c | 58 ++-
> util/iova-tree.c | 161 +++++-
> hw/virtio/meson.build | 2 +-
> 12 files changed, 1852 insertions(+), 135 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
>