Re: [PATCH RFC v4 0/7] virtio-net: add support for SR-IOV emulation

[Yui Washizu <yui.washidu@gmail.com>]

On 2024/04/28 18:05, Akihiko Odaki wrote:
> Based-on: <20240315-reuse-v9-0-67aa69af4d53@daynix.com>
> ("[PATCH for 9.1 v9 00/11] hw/pci: SR-IOV related fixes and improvements")
>
> Introduction
> ------------
>
> This series is based on the RFC series submitted by Yui Washizu[1].
> See also [2] for the context.
>
> This series enables SR-IOV emulation for virtio-net. It is useful
> to test SR-IOV support on the guest, or to expose several vDPA devices
> in a VM. vDPA devices can also provide L2 switching feature for
> offloading though it is out of scope to allow the guest to configure
> such a feature.
>
> The PF side code resides in virtio-pci. The VF side code resides in
> the PCI common infrastructure, but it is restricted to work only for
> virtio-net-pci because of lack of validation.
>
> User Interface
> --------------
>
> A user can configure a SR-IOV capable virtio-net device by adding
> virtio-net-pci functions to a bus. Below is a command line example:
>    -netdev user,id=n -netdev user,id=o
>    -netdev user,id=p -netdev user,id=q
>    -device pcie-root-port,id=b
>    -device virtio-net-pci,bus=b,addr=0x0.0x3,netdev=q,sriov-pf=f
>    -device virtio-net-pci,bus=b,addr=0x0.0x2,netdev=p,sriov-pf=f
>    -device virtio-net-pci,bus=b,addr=0x0.0x1,netdev=o,sriov-pf=f
>    -device virtio-net-pci,bus=b,addr=0x0.0x0,netdev=n,id=f
>
> The VFs specify the paired PF with "sriov-pf" property. The PF must be
> added after all VFs. It is user's responsibility to ensure that VFs have
> function numbers larger than one of the PF, and the function numbers
> have a consistent stride.


I tried to start a VM with more than 8 VFs allocated using your patch,
but the following error occured and qemu didn't work:
VF function number overflows.

I think the cause of this error is that virtio-net-pci PFs don't have ARI.
(pcie_ari_init is not added to virtio-net-pci when PFs are initialized.)
I think it is possible to add it later,
but how about adding pcie_ari_init ?

As a trial,
adding pcie_ari_init to virtio_pci_realize enabled the creation of more 
than 8 VFs.


>
> Keeping VF instances
> --------------------
>
> A problem with SR-IOV emulation is that it needs to hotplug the VFs as
> the guest requests. Previously, this behavior was implemented by
> realizing and unrealizing VFs at runtime. However, this strategy does
> not work well for the proposed virtio-net emulation; in this proposal,
> device options passed in the command line must be maintained as VFs
> are hotplugged, but they are consumed when the machine starts and not
> available after that, which makes realizing VFs at runtime impossible.
>
> As an strategy alternative to runtime realization/unrealization, this
> series proposes to reuse the code to power down PCI Express devices.
> When a PCI Express device is powered down, it will be hidden from the
> guest but will be kept realized. This effectively implements the
> behavior we need for the SR-IOV emulation.
>
> Summary
> -------
>
> Patch 1 disables ROM BAR, which virtio-net-pci enables by default, for
> VFs.
> Patch 2 makes zero stride valid for 1 VF configuration.
> Patch 3 and 4 adds validations.
> Patch 5 adds user-created SR-IOV VF infrastructure.
> Patch 6 makes virtio-pci work as SR-IOV PF for user-created VFs.
> Patch 7 allows user to create SR-IOV VFs with virtio-net-pci.
>
> [1] https://patchew.org/QEMU/1689731808-3009-1-git-send-email-yui.washidu@gmail.com/
> [2] https://lore.kernel.org/all/5d46f455-f530-4e5e-9ae7-13a2297d4bc5@daynix.com/
>
> Co-developed-by: Yui Washizu <yui.washidu@gmail.com>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> Changes in v4:
> - Added patch "hw/pci: Fix SR-IOV VF number calculation" to fix division
>    by zero reported by Yui Washizu.
> - Rebased.
> - Link to v3: https://lore.kernel.org/r/20240305-sriov-v3-0-abdb75770372@daynix.com
>
> Changes in v3:
> - Rebased.
> - Link to v2: https://lore.kernel.org/r/20231210-sriov-v2-0-b959e8a6dfaf@daynix.com
>
> Changes in v2:
> - Changed to keep VF instances.
> - Link to v1: https://lore.kernel.org/r/20231202-sriov-v1-0-32b3570f7bd6@daynix.com
>
> ---
> Akihiko Odaki (7):
>        hw/pci: Do not add ROM BAR for SR-IOV VF
>        hw/pci: Fix SR-IOV VF number calculation
>        pcie_sriov: Ensure PF and VF are mutually exclusive
>        pcie_sriov: Check PCI Express for SR-IOV PF
>        pcie_sriov: Allow user to create SR-IOV device
>        virtio-pci: Implement SR-IOV PF
>        virtio-net: Implement SR-IOV VF
>
>   include/hw/pci/pci_device.h |   6 +-
>   include/hw/pci/pcie_sriov.h |  19 +++
>   hw/pci/pci.c                |  76 +++++++----
>   hw/pci/pcie_sriov.c         | 298 +++++++++++++++++++++++++++++++++++---------
>   hw/virtio/virtio-net-pci.c  |   1 +
>   hw/virtio/virtio-pci.c      |   7 ++
>   6 files changed, 323 insertions(+), 84 deletions(-)
> ---
> base-commit: 2ac5458086ab61282f30c2f8bdf2ae9a0a06a75d
> change-id: 20231202-sriov-9402fb262be8
>
> Best regards,