Re: [PATCH v8 03/12] PCI: liveupdate: Track incoming preserved PCI devices

[David Matlack]

On Tue, Sep 15, 2026 at 8:31 PM Zhu Yanjun <yanjun.zhu@xxxxxxxxx> wrote:
> 在 2026/7/28 15:09, David Matlack 写道:

> > CONFIG_64BIT is now required to enable CONFIG_PCI_LIVEUPDATE so that the
> > domain and bdf can be guaranteed to fit in an unsigned long and be used
> > as the xarray key.

> > diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> > index 3781e2b5f095..8af20f558086 100644
> > --- a/drivers/pci/Kconfig
> > +++ b/drivers/pci/Kconfig
> > @@ -273,7 +273,7 @@ config VGA_ARB_MAX_GPUS
> >
> >   config PCI_LIVEUPDATE
> >       bool "PCI Live Update Support"
> > -     depends on PCI && LIVEUPDATE
> > +     depends on PCI && LIVEUPDATE && 64BIT
>
> One question about adding 64BIT to the dependency:
>
> As I understand it, enabling CONFIG_64BIT essentially means that we are
> building a 64-bit kernel, and a 32-bit architecture cannot normally
> enable CONFIG_64BIT.
>
> If that is the case, would depends on 64BIT be necessary here? Or is PCI
> Live Update already inherently restricted to 64-bit architectures by the
> existing LIVEUPDATE/architecture configuration, so that this dependency
> would be redundant?
>
> If this problem has already discussed, I am very sorry about this.

The necessity is that the PCI core needs to store more than 32-bits in
the unsigned long xarray key (see the snippet above). The dependency
on CONFIG_64BIT ensures that unsigned long is big enough. We could
probably remove the dependency but I would rather wait until someone
with a 32-bit build has a real use-case for using PCI_LIVEUPDATE
before putting any effort into it.