Re: [PATCH v9 00/13] PCI: liveupdate: PCI core support for Live Update

[Zhu Yanjun]

在 2026/9/22 11:53, David Matlack 写道:
> On Tue, Sep 22, 2026 at 11:36 AM Zhu Yanjun <yanjun.zhu@xxxxxxxxx> wrote:
> > 在 2026/9/18 13:06, David Matlack 写道:
> > > Future Work
> > > -----------
> > >
> > > Following this series, we expect to make further improvements to the PCI
> > > core support for Live Update:
> > >
> > >     - Allow P2P across Live Update by avoiding resizing or moving
> > >       preserved device BARs and preserving all upstream bridge windows.
> > >
> > >     - Support preserving Virtual Functions by preserving SR-IOV
> > >       configuration on PFs and enumerating VFs after Live Update.
> > Preserving the PCIe topology, bus numbers, ACS, and Bus Mastering across
> > kexec is a foundational step for minimizing downtime.
> >
> > As we look toward complete end-to-end support for DMA preservation
> > across Live Update—especially for VFIO device passthrough and dma-buf
> > sharing scenarios—IOMMU table/domain preservation becomes crucial to
> > prevent IOMMU page faults when devices continue performing DMA during kexec.
> >
> > I would like to ask about the current status and roadmap regarding IOMMU
> > Live Update / KHO (Kexec Handover) support:
> >
> > Is there an ongoing effort or RFC series for IOMMU handover / page-table
> > preservation currently in development or under discussion?
> >
> > How is the coordination between the PCI core Live Update mechanisms and
> > the IOMMU subsystem being envisioned for preserving IOVA mappings (e.g.,
> > restoring domains or handing over root tables)?
> >
> > Any pointers to active discussion threads, RFCs, or future plans
> > regarding IOMMU participation in Live Update would be greatly appreciated.
> The first IOMMU series to support Live update, can be found here:
>
>    https://lore.kernel.org/linux-iommu/20260921004834.2601285-1-skhawaja@xxxxxxxxxx/

After cloning the source code from samikhawaja/linux, branch 
iommu/phase1-v5, I tested the VFIO live update functionality in my local 
KVM environment and encountered the following issue.

When I run the following commands to verify that VFIO live update works 
correctly, I get the output shown below.

I am currently testing with VFIO v5 and PCI core v9, and I am not sure 
whether this behavior is expected.

Interestingly, when I revert the following commit:

vfio/pci: Preserve the iommufd state of the vfio cdev

the issue disappears.

Could you please let me know whether this is expected behavior, or 
whether it indicates a problem with the current VFIO live update 
implementation?

"

echo "vfio-pci" > /sys/bus/pci/devices/0000:00:04.0/driver_override

echo "0000:00:04.0" > /sys/bus/pci/drivers/vfio-pci/bind
Preserving device in session
vfio_pci_liveupdate_kexec_test.c:122: Assertion Failure

  Expression: ret == 0
  Observed: 0xffffffffffffffea == 0
  [errno: 22 - Invalid argument]
"

Thanks a lot.

Yanjun Zhu

> The IOMMU series builds on top of the PCI core support (this series)
> and the VFIO series linked further up in the cover letter.

--
Best Regards,
Yanjun.Zhu