On Wed, Nov 25, 2020 at 8:09 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > On 2020/11/21 上午2:50, Eugenio Pérez wrote: > > This series enable vDPA software assisted live migration for vhost-net > > devices. This is a new method of vhost devices migration: Instead of > > relay on vDPA device's dirty logging capability, SW assisted LM > > intercepts dataplane, forwarding the descriptors between VM and device. > > > > In this migration mode, qemu offers a new vring to the device to > > read and write into, and disable vhost notifiers, processing guest and > > vhost notifications in qemu. On used buffer relay, qemu will mark the > > dirty memory as with plain virtio-net devices. This way, devices does > > not need to have dirty page logging capability. > > > > This series is a POC doing SW LM for vhost-net devices, which already > > have dirty page logging capabilities. None of the changes have actual > > effect with current devices until last two patches (26 and 27) are > > applied, but they can be rebased on top of any other. These checks the > > device to meet all requirements, and disable vhost-net devices logging > > so migration goes through SW LM. This last patch is not meant to be > > applied in the final revision, it is in the series just for testing > > purposes. > > > > For use SW assisted LM these vhost-net devices need to be instantiated: > > * With IOMMU (iommu_platform=on,ats=on) > > * Without event_idx (event_idx=off) > > > So a question is at what level do we want to implement qemu assisted > live migration. To me it could be done at two levels: > > 1) generic vhost level which makes it work for both vhost-net/vhost-user > and vhost-vDPA > 2) a specific type of vhost > > To me, having a generic one looks better but it would be much more > complicated. So what I read from this series is it was a vhost kernel > specific software assisted live migration which is a good start. > Actually it may even have real use case, e.g it can save dirty bitmaps > for guest with large memory. But we need to address the above > limitations first. > > So I would like to know what's the reason for mandating iommu platform > and ats? And I think we need to fix case of event idx support. > There is no specific reason for mandating iommu & ats, it was just started that way. I will extend the patch to support those cases too. > > > > > Just the notification forwarding (with no descriptor relay) can be > > achieved with patches 7 and 9, and starting migration. Partial applies > > between 13 and 24 will not work while migrating on source, and patch > > 25 is needed for the destination to resume network activity. > > > > It is based on the ideas of DPDK SW assisted LM, in the series of > > > Actually we're better than that since there's no need the trick like > hardcoded IOVA for mediated(shadow) virtqueue. > > > > DPDK's https://patchwork.dpdk.org/cover/48370/ . > > > I notice that you do GPA->VA translations and try to establish a VA->VA > (use VA as IOVA) mapping via device IOTLB. This shortcut should work for > vhost-kernel/user but not vhost-vDPA. The reason is that there's no > guarantee that the whole 64bit address range could be used as IOVA. One > example is that for hardware IOMMU like intel, it usually has 47 or 52 > bits of address width. > > So we probably need an IOVA allocator that can make sure the IOVA is not > overlapped and fit for [1]. We can probably build the IOVA for guest VA > via memory listeners. Then we have > > 1) IOVA for GPA > 2) IOVA for shadow VQ > > And advertise IOVA to VA mapping to vhost. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1b48dc03e575a872404f33b04cd237953c5d7498 > Got it, will control it too. Maybe for vhost-net we could directly send iotlb miss for [0,~0ULL]. > > > > > Comments are welcome. > > > > Thanks! > > > > Eugenio Pérez (27): > > vhost: Add vhost_dev_can_log > > vhost: Add device callback in vhost_migration_log > > vhost: Move log resize/put to vhost_dev_set_log > > vhost: add vhost_kernel_set_vring_enable > > vhost: Add hdev->dev.sw_lm_vq_handler > > virtio: Add virtio_queue_get_used_notify_split > > vhost: Route guest->host notification through qemu > > vhost: Add a flag for software assisted Live Migration > > vhost: Route host->guest notification through qemu > > vhost: Allocate shadow vring > > virtio: const-ify all virtio_tswap* functions > > virtio: Add virtio_queue_full > > vhost: Send buffers to device > > virtio: Remove virtio_queue_get_used_notify_split > > vhost: Do not invalidate signalled used > > virtio: Expose virtqueue_alloc_element > > vhost: add vhost_vring_set_notification_rcu > > vhost: add vhost_vring_poll_rcu > > vhost: add vhost_vring_get_buf_rcu > > vhost: Return used buffers > > vhost: Add vhost_virtqueue_memory_unmap > > vhost: Add vhost_virtqueue_memory_map > > vhost: unmap qemu's shadow virtqueues on sw live migration > > vhost: iommu changes > > vhost: Do not commit vhost used idx on vhost_virtqueue_stop > > vhost: Add vhost_hdev_can_sw_lm > > vhost: forbid vhost devices logging > > > > hw/virtio/vhost-sw-lm-ring.h | 39 +++ > > include/hw/virtio/vhost.h | 5 + > > include/hw/virtio/virtio-access.h | 8 +- > > include/hw/virtio/virtio.h | 4 + > > hw/net/virtio-net.c | 39 ++- > > hw/virtio/vhost-backend.c | 29 ++ > > hw/virtio/vhost-sw-lm-ring.c | 268 +++++++++++++++++++ > > hw/virtio/vhost.c | 431 +++++++++++++++++++++++++----- > > hw/virtio/virtio.c | 18 +- > > hw/virtio/meson.build | 2 +- > > 10 files changed, 758 insertions(+), 85 deletions(-) > > create mode 100644 hw/virtio/vhost-sw-lm-ring.h > > create mode 100644 hw/virtio/vhost-sw-lm-ring.c > > > So this looks like a pretty huge patchset which I'm trying to think of > ways to split. An idea is to do this is two steps > > 1) implement a shadow virtqueue mode for vhost first (w/o live > migration). Then we can test descriptors relay, IOVA allocating, etc. How would that mode be activated if it is not tied to live migration? New backend/command line switch? Maybe it is better to also start with no iommu & ats support and add it on top. > 2) add live migration support on top > > And it looks to me it's better to split the shadow virtqueue (virtio > driver part) into an independent file. And use generic name (w/o > "shadow") in order to be reused by other use cases as well. > I think the same. Thanks! > Thoughts? >
