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

[Eugenio Perez Martin]

On Fri, Oct 29, 2021 at 8:41 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> 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.
>
> 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
>
> --
> 2.27.0
>
>
>

To make the review easier, this tree is also at [1].

Thanks!

[1] https://github.com/eugpermar/qemu/tree/vdpa_sw_live_migration.d/vdpa-v5