On Tue, Mar 08, 2022 at 09:15:37AM +0100, Eugenio Perez Martin
wrote:> On Tue, Mar 8, 2022 at 8:55 AM Michael S. Tsirkin <mst at redhat.com>
wrote:
> >
> > On Tue, Mar 08, 2022 at 03:34:17PM +0800, Jason Wang wrote:
> > > On Tue, Mar 8, 2022 at 3:28 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> > > >
> > > > On Tue, Mar 08, 2022 at 03:14:35PM +0800, Jason Wang wrote:
> > > > > On Tue, Mar 8, 2022 at 3:11 PM Michael S. Tsirkin
<mst at redhat.com> wrote:
> > > > > >
> > > > > > On Tue, Mar 08, 2022 at 02:03:32PM +0800, Jason
Wang wrote:
> > > > > > >
> > > > > > > ? 2022/3/7 ??11:33, Eugenio P?rez ??:
> > > > > > > > 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.
> > > > > > > >
> > > > > > > > SVQ needs to be enabled with cmdline:
> > > > > > > >
> > > > > > > > -netdev
type=vhost-vdpa,vhostdev=vhost-vdpa-0,id=vhost-vdpa0,svq=on
> > > > > >
> > > > > > A stable API for an incomplete feature is a
problem imho.
> > > > >
> > > > > It should be "x-svq".
> > > >
> > > >
> > > > Well look at patch 15.
> > >
> > > It's a bug that needs to be fixed.
> > >
> > > >
> > > > > >
> > > > > >
> > > > > > > >
> > > > > > > > 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 ~9009.96Mbps:
> > > > > > > > Recv Send Send
> > > > > > > > Socket Socket Message Elapsed
> > > > > > > > Size Size Size Time
Throughput
> > > > > > > > bytes bytes bytes secs.
10^6bits/sec
> > > > > > > > 131072 16384 16384 30.01 9061.03
> > > > > > > > 131072 16384 16384 30.01 8962.94
> > > > > > > > 131072 16384 16384 30.01 9005.92
> > > > > > > >
> > > > > > > > To enable SVQ buffers forwarding reduce
throughput to about
> > > > > > > > Recv Send Send
> > > > > > > > Socket Socket Message Elapsed
> > > > > > > > Size Size Size Time
Throughput
> > > > > > > > bytes bytes bytes secs.
10^6bits/sec
> > > > > > > > 131072 16384 16384 30.01 7689.72
> > > > > > > > 131072 16384 16384 30.00 7752.07
> > > > > > > > 131072 16384 16384 30.01 7750.30
> > > > > > > >
> > > > > > > > However, many performance improvements
were left out of this series for
> > > > > > > > simplicity, so difference should shrink
in the future.
> > > > > > > >
> > > > > > > > Comments are welcome.
> > > > > > >
> > > > > > >
> > > > > > > Hi Michael:
> > > > > > >
> > > > > > > What do you think of this series? It looks
good to me as a start. The
> > > > > > > feature could only be enabled as a dedicated
parameter. If you're ok, I'd
> > > > > > > try to make it for 7.0.
> > > > > > >
> > > > > > > Thanks
> > > > > >
> > > > > > Well that's cutting it awfully close, and
it's not really useful
> > > > > > at the current stage, is it?
> > > > >
> > > > > This allows vDPA to be migrated when using
"x-svq=on".
> > > > > But anyhow it's
> > > > > experimental.
> > > >
> > > > it's less experimental than incomplete. It seems pretty
clearly not
> > > > the way it will work down the road, we don't want svq
involved
> > > > at all times.
> > >
> > > Right, but SVQ could be used for other places e.g providing
migration
> > > compatibility when the destination lacks some features.
> >
> > In its current form? I don't see how. Generally? Maybe but I
suspect
> > we'll have to rework it completely for that.
> >
>
> RFCs of the series already do that: guest to SVQ communication
> supported indirect descriptors and packed virtqueue but SVQ to device
> did not. Even SVQ vring size could be different from guest's vring
> size. It's not a big diff actually, I can send it as a RFC on top of
> this to show it.
>
> But that part was left out for simplicity and added as a TODO, so it
> just negotiates one set of features instead of two.
>
> > > >
> > > > > >
> > > > > > The IOVA trick does not feel complete either.
> > > > >
> > > > > I don't get here. We don't use any IOVA trick
as DPDK (it reserve IOVA
> > > > > for shadow vq) did. So we won't suffer from the
issues of DPDK.
> > > > >
> > > > > Thanks
> > > >
> > > > Maybe I misundrstand how this all works.
> > > > I refer to all the iova_tree_alloc_map things.
> > >
> > > It's a simple IOVA allocater actually. Anything wrong with
that?
> >
> > Not by itself but I'm not sure we can guarantee guest will not
> > attempt to use the IOVA addresses we are reserving down
> > the road.
> >
>
> The SVQ vring (the one that device's see) does not use GPA addresses
> anymore, but this new iova space. If the guest tries to expose a
> writable buffer with the address of SVQ vring, VirtQueue would refuse
> to translate it, generating an error. The same way it would generate
> an error with emulated devices.
Right. But guests are not really set up to handle such
errors except by failing the transaction, are they?
> If we hot-plug more physical memory to the guest, this new range is
> added as a totally new iova entry, which cannot collide with previous
> entries, both GPA and SVQ. Same thing happens if the vhost device is
> added or removed, or if the guest reset or start (set DRIVER_OK) the
> device.
>
> Thanks!
>
> > > I'm fine with making it for the future release.
> > >
> > > Thanks
> > >
> > > >
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > TODO on 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 v4:
> > > > > > > > * Iterate iova->hva tree instead on
maintain own tree so we support HVA
> > > > > > > > overlaps.
> > > > > > > > * Fix: Errno completion at failure.
> > > > > > > > * Rename x-svq to svq, so changes to
stable does not affect cmdline parameter.
> > > > > > > >
> > > > > > > > Changes from v3:
> > > > > > > > * Add @unstable feature to
NetdevVhostVDPAOptions.x-svq.
> > > > > > > > * Fix uncomplete mapping (by 1 byte) of
memory regions if svq is enabled.
> > > > > > > > v3 link:
> > > > > > > >
https://lore.kernel.org/qemu-devel/20220302203012.3476835-1-eperezma at
redhat.com/
> > > > > > > >
> > > > > > > > Changes from v2:
> > > > > > > > * Less assertions and more error
handling in iova tree code.
> > > > > > > > * Better documentation, both fixing
errors and making @param: format
> > > > > > > > * Homogeneize SVQ avail_idx_shadow and
shadow_used_idx to make shadow a
> > > > > > > > prefix at both times.
> > > > > > > > * Fix: Fo not use
VirtQueueElement->len field, track separatedly.
> > > > > > > > * Split
vhost_svq_{enable,disable}_notification, so the code looks more
> > > > > > > > like the kernel driver code.
> > > > > > > > * Small improvements.
> > > > > > > > v2 link:
> > > > > > > >
https://lore.kernel.org/all/CAJaqyWfXHE0C54R_-OiwJzjC0gPpkE3eX0L8BeeZXGm1ERYPtA
at mail.gmail.com/
> > > > > > > >
> > > > > > > > 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 at
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 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 (15):
> > > > > > > > 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_svq_get_vring_addr
> > > > > > > > vdpa: adapt vhost_ops callbacks to
svq
> > > > > > > > vhost: Shadow virtqueue buffers
forwarding
> > > > > > > > util: Add iova_tree_alloc_map
> > > > > > > > util: add iova_tree_find_iova
> > > > > > > > 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 |
8 +-
> > > > > > > > hw/virtio/vhost-iova-tree.h |
27 ++
> > > > > > > > hw/virtio/vhost-shadow-virtqueue.h |
87 ++++
> > > > > > > > include/hw/virtio/vhost-vdpa.h |
8 +
> > > > > > > > include/qemu/iova-tree.h |
38 +-
> > > > > > > > hw/virtio/vhost-iova-tree.c |
110 +++++
> > > > > > > > hw/virtio/vhost-shadow-virtqueue.c |
637 +++++++++++++++++++++++++++++
> > > > > > > > hw/virtio/vhost-vdpa.c |
525 +++++++++++++++++++++++-
> > > > > > > > net/vhost-vdpa.c |
48 ++-
> > > > > > > > util/iova-tree.c |
169 ++++++++
> > > > > > > > hw/virtio/meson.build |
2 +-
> > > > > > > > 11 files changed, 1633 insertions(+),
26 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
> > > > > > > >
> > > > > >
> > > >
> >