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/7d86c715-6d71-8a27-91f5-8d47b71e3201@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-eperezma@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