Re: [PATCH v7 resend 0/4] add generic vDPA device support

[Longpeng (Mike, Cloud Infrastructure Service Product Dept.)]

在 2022/11/6 21:47, Michael S. Tsirkin 写道:
> On Sun, Nov 06, 2022 at 09:11:39PM +0800, Longpeng (Mike, Cloud Infrastructure 
> Service Product Dept.) wrote:
> > 在 2022/11/6 13:22, Michael S. Tsirkin 写道:
> > > On Sun, Nov 06, 2022 at 08:17:07AM +0800, Longpeng (Mike, Cloud Infrastructure 
> > > Service Product Dept.) wrote:
> > > > 在 2022/11/6 0:43, Michael S. Tsirkin 写道:
> > > > > On Sat, Nov 05, 2022 at 04:36:25PM +0800, Longpeng(Mike) wrote:
> > > > > > From: Longpeng <longpeng2@huawei.com>
> > > > > >
> > > > > > Hi guys,
> > > > > >
> > > > > > With the generic vDPA device, QEMU won't need to touch the device
> > > > > > types any more, such like vfio.
> > > > >
> > > > > With this kind of passthrough migration is completely MIA right?
> > > > > Better add a blocker...
> > > >
> > > > Oh, I missed the "vdpa-dev: mark the device as unmigratable" since v4 and
> > > > I'll add it in the next version.
> > > >
> > > > We'll support passthrough migration in the next step. We have already
> > > > written a demo that can migrate between some offloading cards.
> > >
> > > Hmm ok. Backend disconnect can't work though, can it? State
> > > is by necessity lost when backend crashes.
> > > Yes, it can't.
> >
> > > > > And given this is there an advantage over VFIO?
> > > >
> > > > I think the answer is the same as "why we need vDPA" if we compare it with
> > > > VFIO.
> > >
> > > The answer is mostly because you can migrate and support backend
> > > disconnect, no?
> > Migrating between different hardware is the first consideration in our
> > requirement, supporting backend disconnect is a low priority.
>
> I dislike non-orthogonal features though ...
> And the advantage of keeping it out of process with qemu is
> I presume security?

Yes, this is one of the reasons. The TCB of the generic vdpa device is 
smaller than the existing vdpa device (needs to use the 
virtio-net/blk/scsi emulation codes).

Besides, the generic vdpa device can support any virtio device, but the 
existing vdpa device only supports virtio-net yet.

Though the existing vdpa device is more powerful and the generic vdpa 
device would miss some features, it can be an alternative for some users.


> > > > > > We can use the generic vDPA device as follow:
> > > > > >      -device vhost-vdpa-device-pci,vhostdev=/dev/vhost-vdpa-X
> > > > > >      Or
> > > > > >      -M microvm -m 512m -smp 2 -kernel ... -initrd ... -device \
> > > > > >      vhost-vdpa-device,vhostdev=/dev/vhost-vdpa-x
> > > > >
> > > > > > Changes v6 -> v7:
> > > > > >        (v6: https://mail.gnu.org/archive/html/qemu-devel/2022-05/msg02821.html)
> > > > > >        - rebase. [Jason]
> > > > > >        - add documentation . [Stefan]
> > > > > >
> > > > > > Changes v5 -> v6:
> > > > > >      Patch 2:
> > > > > >        - Turn to the original approach in the RFC to initialize the
> > > > > >          virtio_pci_id_info array. [Michael]
> > > > > >           https://lore.kernel.org/all/20220105005900.860-2-longpeng2@huawei.com/
> > > > > >      Patch 3:
> > > > > >        - Fix logical error of exception handler around the post_init.
> > > > > >          [Stefano]
> > > > > >        - Fix some coding style warnings. [Stefano]
> > > > > >      Patch 4:
> > > > > >        - Fix some coding style warnings. [Stefano]
> > > > > >
> > > > > > Changes v4 -> v5:
> > > > > >      Patch 3:
> > > > > >        - remove vhostfd [Jason]
> > > > > >        - support virtio-mmio [Jason]
> > > > > >
> > > > > > Changes v3 -> v4:
> > > > > >      v3: https://www.mail-archive.com/qemu-devel@nongnu.org/msg877015.html
> > > > > >      - reorganize the series [Stefano]
> > > > > >      - fix some typos [Stefano]
> > > > > >      - fix logical error in vhost_vdpa_device_realize [Stefano]
> > > > > >
> > > > > > Changes v2 -> v3
> > > > > >      Patch 4 & 5:
> > > > > >        - only call vdpa ioctls in vdpa-dev.c [Stefano, Longpeng]
> > > > > >        - s/VQS_NUM/VQS_COUNT  [Stefano]
> > > > > >        - check both vdpa_dev_fd and vdpa_dev [Stefano]
> > > > > >      Patch 6:
> > > > > >        - move all steps into vhost_vdpa_device_unrealize. [Stefano]
> > > > > >
> > > > > > Changes RFC -> v2
> > > > > >      Patch 1:
> > > > > >        - rename 'pdev_id' to 'trans_devid'  [Michael]
> > > > > >        - only use transitional device id for the devices
> > > > > >          listed in the spec  [Michael]
> > > > > >        - use macros to make the id_info table clearer  [Longpeng]
> > > > > >        - add some modern devices in the id_info table  [Longpeng]
> > > > > >      Patch 2:
> > > > > >        - remove the GET_VECTORS_NUM command  [Jason]
> > > > > >      Patch 4:
> > > > > >        - expose vdpa_dev_fd as a QOM preperty  [Stefan]
> > > > > >        - introduce vhost_vdpa_device_get_u32 as a common
> > > > > >          function to make the code clearer  [Stefan]
> > > > > >        - fix the misleading description of 'dc->desc'  [Stefano]
> > > > > >      Patch 5:
> > > > > >        - check returned number of virtqueues  [Stefan]
> > > > > >      Patch 6:
> > > > > >        - init s->num_queues  [Stefano]
> > > > > >        - free s->dev.vqs  [Stefano]
> > > > > >
> > > > > >
> > > > > > Longpeng (Mike) (4):
> > > > > >      virtio: get class_id and pci device id by the virtio id
> > > > > >      vdpa: add vdpa-dev support
> > > > > >      vdpa: add vdpa-dev-pci support
> > > > > >      docs: Add generic vhost-vdpa device documentation
> > > > > >
> > > > > >     docs/system/devices/vhost-vdpa-device.rst |  43 +++
> > > > > >     hw/virtio/Kconfig                         |   5 +
> > > > > >     hw/virtio/meson.build                     |   2 +
> > > > > >     hw/virtio/vdpa-dev-pci.c                  | 102 ++++++
> > > > > >     hw/virtio/vdpa-dev.c                      | 377 ++++++++++++++++++++++
> > > > > >     hw/virtio/virtio-pci.c                    |  88 +++++
> > > > > >     include/hw/virtio/vdpa-dev.h              |  43 +++
> > > > > >     include/hw/virtio/virtio-pci.h            |   5 +
> > > > > >     8 files changed, 665 insertions(+)
> > > > > >     create mode 100644 docs/system/devices/vhost-vdpa-device.rst
> > > > > >     create mode 100644 hw/virtio/vdpa-dev-pci.c
> > > > > >     create mode 100644 hw/virtio/vdpa-dev.c
> > > > > >     create mode 100644 include/hw/virtio/vdpa-dev.h
> > > > > >
> > > > > > --
> > > > > > 2.23.0
> > > > >
> > > > > .
> > >
> > >
> > > .
>
>
> .