Re: [PATCH RFC v2 00/12] virtio-net: add support for SR-IOV emulation

[Yui Washizu]

On 2023/12/10 13:05, Akihiko Odaki wrote:
> 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 attempted to create a VF on a VM using your patches and
tested the creation of one VF on the VM.
I initiated QEMU with the following commands:
-netdev tap,id=n,vhost=on -netdev tap,id=o,vhost=on
-device pcie-root-port,id=b
-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

However, when creating just one VF,
QEMU crashed at hw/pci/pci.c:1443.
---
uint32_t vf_num = (d->devfn - (pf->devfn + vf_offset)) / vf_stride;
---
The error output was:
'CPU 1/KVM trap divide error ip:... sp:... error:0 in kvm-qemu.'

Interestingly, when creating two VFs, QEMU did not crash.

> 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, 5] refactors the PCI infrastructure code.
> Patch [6, 10] adds user-created SR-IOV VF infrastructure.
> Patch 11 makes virtio-pci work as SR-IOV PF for user-created VFs.
> Patch 12 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 v2:
> - Changed to keep VF instances.
> - Link to v1: 
> 20231202-sriov-v1-0-32b3570f7bd6@daynix.com">https://lore.kernel.org/r/20231202-sriov-v1-0-32b3570f7bd6@daynix.com
>
> ---
> Akihiko Odaki (12):
>        hw/pci: Initialize PCI multifunction after realization
>        hw/pci: Determine if rombar is explicitly enabled
>        hw/pci: Do not add ROM BAR for SR-IOV VF
>        vfio: Avoid inspecting option QDict for rombar
>        hw/qdev: Remove opts member
>        pcie_sriov: Reuse SR-IOV VF device instances
>        pcie_sriov: Release VFs failed to realize
>        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
>
>   docs/pcie_sriov.txt         |   8 +-
>   include/hw/pci/pci.h        |   2 +-
>   include/hw/pci/pci_device.h |  13 +-
>   include/hw/pci/pcie_sriov.h |  25 ++-
>   include/hw/qdev-core.h      |   4 -
>   hw/core/qdev.c              |   1 -
>   hw/net/igb.c                |   3 +-
>   hw/nvme/ctrl.c              |   3 +-
>   hw/pci/pci.c                |  98 +++++++-----
>   hw/pci/pci_host.c           |   4 +-
>   hw/pci/pcie.c               |   4 +-
>   hw/pci/pcie_sriov.c         | 360 +++++++++++++++++++++++++++++++++-----------
>   hw/vfio/pci.c               |   3 +-
>   hw/virtio/virtio-net-pci.c  |   1 +
>   hw/virtio/virtio-pci.c      |   7 +
>   system/qdev-monitor.c       |  12 +-
>   16 files changed, 395 insertions(+), 153 deletions(-)
> ---
> base-commit: 4705fc0c8511d073bee4751c3c974aab2b10a970
> change-id: 20231202-sriov-9402fb262be8
>
> Best regards,