Re: [PATCH v2 00/10] LUO: PCI subsystem (phase I)

Chris Li
2025-10-09T17:13:08Z

On Wed, Oct 8, 2025 at 4:01 PM David Matlack <dmatlack@google.com> wrote:
>
> On Tue, Oct 7, 2025 at 4:32 PM Chris Li <chrisl@kernel.org> wrote:
> >
> > Thanks to one that provides good feedback on the PCI series.
> >
> > I just want to give an update on the state of the LUO PCI series,
> > based on the feedback I received. The LUO PCI series should be called
> > from the memfd side and remove global subsystem state if possible.
>
> By "memfd side" I believe you are referring to LUO fd preservation
> (likely the VFIO cdev fd).

Yes. I haven't taken a closer look at the recent LUO fd preservation
series. It is on my to do list, now I am depending on it.

> > Which means the PCI series will depend on the VIFO or iommu series.
> > I have some internal alignment with Vipin (for VFIO) and Samiullah
> > (for iommu). Here is the new plan for upstream patch submission:
> >
> > 1) KHO series go first, which is already happening with additional improvement.
> >
> > 2) Next is Pasha's LUO series with memfd support, also happening right now.
> >
> > 3) Next series will be Vipin's VFIO series with preserving one
> > busmaster bit in the config space of the end point vfio device, there
> > is no PCI layer involved yet. The VFIO will use some driver trick to
> > prevent the native driver from binding to the liveupdate device used
> > by VFIO after kexec. After kexec, the VFIO driver validates that the
> > busmaster in the PCI config register is already set.
>
> Yes. Last we discussed Vipin is planning to just compile out the
> native driver of the device he is using to test. So we don't expect to
> need any kernel code changes to unblock basic testing and posting the
> RFC.

Ack.

>
> >
> > 4) After the VFIO series, the PCI can start to preserve the livedupate
> > device by BDF. Avoid the driver auto probe on the livedupate devices.
> > At this point the VFIO driver in stage 3 will not need the other
> > driver trick to avoid the auto bind of native driver. The PCI layer
> > takes the core of that. This series PCI will have very limited
> > support, most of the driver callback is not needed, no bridge device
> > dependent as well.
>
> I suspect we'll need the new file-lifecycle-bound global state thing
> that Pasha is working on [1] to accomplish this. So please track
> LUOv5+ as a dependency for this.
>
> [1] https://lore.kernel.org/lkml/CA+CK2bB+RdapsozPHe84MP4NVSPLo6vje5hji5MKSg8L6ViAbw@mail.gmail.com/

Agree, I need to figure out the boiler plate change to hook up PCI to
the file descriptors.

Thanks for the clarification.

Chris