Re: [RFC PATCH v8 00/21] Net Control VQ support with asid in vDPA SVQ

[Jason Wang <jasowang@redhat.com>]

On Tue, Jun 14, 2022 at 12:32 AM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Wed, Jun 8, 2022 at 9:28 PM Eugenio Perez Martin <eperezma@redhat.com> wrote:
> >
> > On Wed, Jun 8, 2022 at 7:51 AM Jason Wang <jasowang@redhat.com> wrote:
> > >
> > >
> > > 在 2022/5/20 03:12, Eugenio Pérez 写道:
> > > > Control virtqueue is used by networking device for accepting various
> > > > commands from the driver. It's a must to support multiqueue and other
> > > > configurations.
> > > >
> > > > Shadow VirtQueue (SVQ) already makes possible migration of virtqueue
> > > > states, effectively intercepting them so qemu can track what regions of memory
> > > > are dirty because device action and needs migration. However, this does not
> > > > solve networking device state seen by the driver because CVQ messages, like
> > > > changes on MAC addresses from the driver.
> > > >
> > > > To solve that, this series uses SVQ infraestructure proposed to intercept
> > > > networking control messages used by the device. This way, qemu is able to
> > > > update VirtIONet device model and to migrate it.
> > > >
> > > > However, to intercept all queues would slow device data forwarding. To solve
> > > > that, only the CVQ must be intercepted all the time. This is achieved using
> > > > the ASID infraestructure, that allows different translations for different
> > > > virtqueues. The most updated kernel part of ASID is proposed at [1].
> > > >
> > > > You can run qemu in two modes after applying this series: only intercepting
> > > > cvq with x-cvq-svq=on or intercept all the virtqueues adding cmdline x-svq=on:
> > > >
> > > > -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-cvq-svq=on,x-svq=on
> > > >
> > > > First three patches enable the update of the virtio-net device model for each
> > > > CVQ message acknoledged by the device.
> > > >
> > > > Patches from 5 to 9 enables individual SVQ to copy the buffers to QEMU's VA.
> > > > This allows simplyfing the memory mapping, instead of map all the guest's
> > > > memory like in the data virtqueues.
> > > >
> > > > Patch 10 allows to inject control messages to the device. This allows to set
> > > > state to the device both at QEMU startup and at live migration destination. In
> > > > the future, this may also be used to emulate _F_ANNOUNCE.
> > > >
> > > > Patch 11 updates kernel headers, but it assign random numbers to needed ioctls
> > > > because they are still not accepted in the kernel.
> > > >
> > > > Patches 12-16 enables the set of the features of the net device model to the
> > > > vdpa device at device start.
> > > >
> > > > Last ones enables the sepparated ASID and SVQ.
> > > >
> > > > Comments are welcomed.
> > >
> > >
> > > As discussed, I think we need to split this huge series into smaller ones:
> > >
> > > 1) shadow CVQ only, this makes rx-filter-event work
> > > 2) ASID support for CVQ
> > >
> > > And for 1) we need consider whether or not it could be simplified.
> > >
> > > Or do it in reverse order, since if we do 1) first, we may have security
> > > issues.
> > >
> >
> > I'm ok with both, but I also think 2) before 1) might make more sense.
> > There is no way to only shadow CVQ otherwise ATM.
> >
>
> On second thought, that order is kind of harder.
>
> If we only map CVQ buffers, we need to either:
> a. Copy them to controlled buffers
> b. Track properly when to unmap them

Just to make sure we're at the same page:

I meant we can start with e.g having a dedicated ASID for CVQ but
still using CVQ passthrough.

Then do other stuff on top.

>
> Alternative a. have the same problems exposed in this RFC: It's hard
> (and unneeded in the final version) to know the size to copy.
> Alternative b. also requires things not needed in the final version,
> like to count the number of times each page is mapped and unmapped.
>
> So I'll go to the first alternative, that is also the proposed order
> of the RFC. What security issues do you expect beyond the comments in
> this series?

If we shadow CVQ without ASID. The guest may guess the IOVA of CVQ and
try to peek/modify it?

Thanks

>
> Thanks!
>
> > Can we do as with previous base SVQ patches? they were merged although
> > there is still no way to enable SVQ.
> >
> > Thanks!
> >
> > > Thoughts?
> > >
> > > Thanks
> > >
> > >
> > > >
> > > > TODO:
> > > > * Fallback on regular CVQ if QEMU cannot isolate in its own ASID by any
> > > >    reason, blocking migration. This is tricky, since it can cause that the VM
> > > >    cannot be migrated anymore, so some way of block it must be used.
> > > > * Review failure paths, some are with TODO notes, other don't.
> > > >
> > > > Changes from rfc v7:
> > > > * Don't map all guest space in ASID 1 but copy all the buffers. No need for
> > > >    more memory listeners.
> > > > * Move net backend start callback to SVQ.
> > > > * Wait for device CVQ commands used by the device at SVQ start, avoiding races.
> > > > * Changed ioctls, but they're provisional anyway.
> > > > * Reorder commits so refactor and code adding ones are closer to usage.
> > > > * Usual cleaning: better tracing, doc, patches messages, ...
> > > >
> > > > Changes from rfc v6:
> > > > * Fix bad iotlb updates order when batching was enabled
> > > > * Add reference counting to iova_tree so cleaning is simpler.
> > > >
> > > > Changes from rfc v5:
> > > > * Fixes bad calculus of cvq end group when MQ is not acked by the guest.
> > > >
> > > > Changes from rfc v4:
> > > > * Add missing tracing
> > > > * Add multiqueue support
> > > > * Use already sent version for replacing g_memdup
> > > > * Care with memory management
> > > >
> > > > Changes from rfc v3:
> > > > * Fix bad returning of descriptors to SVQ list.
> > > >
> > > > Changes from rfc v2:
> > > > * Fix use-after-free.
> > > >
> > > > Changes from rfc v1:
> > > > * Rebase to latest master.
> > > > * Configure ASID instead of assuming cvq asid != data vqs asid.
> > > > * Update device model so (MAC) state can be migrated too.
> > > >
> > > > [1] https://lkml.kernel.org/kvm/20220224212314.1326-1-gdawar@xilinx.com/
> > > >
> > > > Eugenio Pérez (21):
> > > >    virtio-net: Expose ctrl virtqueue logic
> > > >    vhost: Add custom used buffer callback
> > > >    vdpa: control virtqueue support on shadow virtqueue
> > > >    virtio: Make virtqueue_alloc_element non-static
> > > >    vhost: Add vhost_iova_tree_find
> > > >    vdpa: Add map/unmap operation callback to SVQ
> > > >    vhost: move descriptor translation to vhost_svq_vring_write_descs
> > > >    vhost: Add SVQElement
> > > >    vhost: Add svq copy desc mode
> > > >    vhost: Add vhost_svq_inject
> > > >    vhost: Update kernel headers
> > > >    vdpa: delay set_vring_ready after DRIVER_OK
> > > >    vhost: Add ShadowVirtQueueStart operation
> > > >    vhost: Make possible to check for device exclusive vq group
> > > >    vhost: add vhost_svq_poll
> > > >    vdpa: Add vhost_vdpa_start_control_svq
> > > >    vdpa: Add asid attribute to vdpa device
> > > >    vdpa: Extract get features part from vhost_vdpa_get_max_queue_pairs
> > > >    vhost: Add reference counting to vhost_iova_tree
> > > >    vdpa: Add x-svq to NetdevVhostVDPAOptions
> > > >    vdpa: Add x-cvq-svq
> > > >
> > > >   qapi/net.json                                |  13 +-
> > > >   hw/virtio/vhost-iova-tree.h                  |   7 +-
> > > >   hw/virtio/vhost-shadow-virtqueue.h           |  61 ++-
> > > >   include/hw/virtio/vhost-vdpa.h               |   3 +
> > > >   include/hw/virtio/vhost.h                    |   3 +
> > > >   include/hw/virtio/virtio-net.h               |   4 +
> > > >   include/hw/virtio/virtio.h                   |   1 +
> > > >   include/standard-headers/linux/vhost_types.h |  11 +-
> > > >   linux-headers/linux/vhost.h                  |  25 +-
> > > >   hw/net/vhost_net.c                           |   5 +-
> > > >   hw/net/virtio-net.c                          |  84 +++--
> > > >   hw/virtio/vhost-iova-tree.c                  |  35 +-
> > > >   hw/virtio/vhost-shadow-virtqueue.c           | 378 ++++++++++++++++---
> > > >   hw/virtio/vhost-vdpa.c                       | 206 +++++++++-
> > > >   hw/virtio/virtio.c                           |   2 +-
> > > >   net/vhost-vdpa.c                             | 294 ++++++++++++++-
> > > >   hw/virtio/trace-events                       |  10 +-
> > > >   17 files changed, 1012 insertions(+), 130 deletions(-)
> > > >
> > >
>