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

[Pratyush Yadav <pratyush@kernel.org>]

On Wed, Sep 16 2026, David Matlack wrote:

> On Tue, Sep 15, 2026 at 8:31 PM Zhu Yanjun <yanjun.zhu@linux.dev> 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.

KHO or live update themselves don't support 32-bit platforms and there
are no plans to do so either. So I don't think you even need to have a
dependency on 64BIT in PCI_LIVEUPDATE. Only 64 bit architectures define
ARCH_SUPPORTS_KEXEC_HANDOVER, so PCI_LIVEUPDATE and others indirectly
inherit the dependency.

If you'd like to be extra safe, then probably you should add a
dependency to 64BIT in KEXEC_HANDOVER directly. Though I think that can
be a separate patch independent from this series.

-- 
Regards,
Pratyush Yadav