Re: [RFC PATCH v5 00/26] vDPA shadow virtqueue

[Eugenio Perez Martin <eperezma@redhat.com>]

On Tue, Nov 2, 2021 at 5:26 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2021/10/30 上午2:34, Eugenio Pérez 写道:
> > 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, 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 supports packed vring and not split and old guest
> > 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.
> >
> > For qemu to use shadow virtqueues the guest virtio driver must not use
> > features like event_idx.
> >
> > SVQ needs to be enabled with QMP command:
> >
> > { "execute": "x-vhost-set-shadow-vq",
> >        "arguments": { "name": "vhost-vdpa0", "enable": true } }
> >
> > This series includes some patches to delete in the final version that
> > helps with its testing. The first two of the series have been sent
> > sepparately but they haven't been included in qemu main branch.
> >
> > The two after them adds the feature to stop the device and be able to
> > set and get its status. It's intended to be used with vp_vpda driver in
> > a nested environment, so they are also external to this series. The
> > vp_vdpa driver also need modifications to forward the new status bit,
> > they will be proposed sepparately
> >
> > Patches 5-12 prepares the SVQ and QMP command to support guest to host
> > notifications forwarding. If the SVQ is enabled with these ones
> > applied and the device supports it, that part can be tested in
> > isolation (for example, with networking), hopping through SVQ.
> >
> > Same thing is true with patches 13-17, but with device to guest
> > notifications.
> >
> > Based on them, patches from 18 to 22 implement the actual buffer
> > forwarding, using some features already introduced in previous.
> > However, they will need a host device with no iommu, something that
> > is not available at the moment.
> >
> > The last part of the series uses properly the host iommu, so the driver
> > can access this new virtual address space created.
> >
> > Comments are welcome.
>
>
> I think we need do some benchmark to see the performance impact.
>
> Thanks
>

Ok, I will add them for the next revision.

Thanks!

>
> >
> > TODO:
> > * Event, indirect, packed, and others features of virtio.
> > * 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 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 (26):
> >    util: Make some iova_tree parameters const
> >    vhost: Fix last queue index of devices with no cvq
> >    virtio: Add VIRTIO_F_QUEUE_STATE
> >    virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED
> >    vhost: Add x-vhost-set-shadow-vq qmp
> >    vhost: Add VhostShadowVirtqueue
> >    vdpa: Save kick_fd in vhost-vdpa
> >    vdpa: Add vhost_svq_get_dev_kick_notifier
> >    vdpa: Add vhost_svq_set_svq_kick_fd
> >    vhost: Add Shadow VirtQueue kick forwarding capabilities
> >    vhost: Handle host notifiers in SVQ
> >    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: ack VIRTIO_F_QUEUE_STATE if device supports it
> >    vhost: Add vhost_svq_valid_device_features to shadow vq
> >    vhost: Add vhost_svq_valid_guest_features to shadow vq
> >    vhost: Shadow virtqueue buffers forwarding
> >    util: Add iova_tree_alloc
> >    vhost: Add VhostIOVATree
> >    vhost: Use a tree to store memory mappings
> >    vdpa: Add custom IOTLB translations to SVQ
> >
> >   qapi/net.json                                 |  20 +
> >   hw/virtio/vhost-iova-tree.h                   |  27 +
> >   hw/virtio/vhost-shadow-virtqueue.h            |  44 ++
> >   hw/virtio/virtio-pci.h                        |   1 +
> >   include/hw/virtio/vhost-vdpa.h                |  12 +
> >   include/hw/virtio/virtio.h                    |   4 +-
> >   include/qemu/iova-tree.h                      |  25 +-
> >   .../standard-headers/linux/virtio_config.h    |   5 +
> >   include/standard-headers/linux/virtio_pci.h   |   2 +
> >   hw/i386/intel_iommu.c                         |   2 +-
> >   hw/net/vhost_net.c                            |   2 +-
> >   hw/net/virtio-net.c                           |   6 +-
> >   hw/virtio/vhost-iova-tree.c                   | 157 ++++
> >   hw/virtio/vhost-shadow-virtqueue.c            | 746 ++++++++++++++++++
> >   hw/virtio/vhost-vdpa.c                        | 437 +++++++++-
> >   hw/virtio/virtio-pci.c                        |  16 +-
> >   net/vhost-vdpa.c                              |  28 +
> >   util/iova-tree.c                              | 151 +++-
> >   hw/virtio/meson.build                         |   2 +-
> >   19 files changed, 1664 insertions(+), 23 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
> >
>