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

[Chris Li <chrisl@kernel.org>]

On Mon, Oct 13, 2025 at 6:58 AM Pratyush Yadav <pratyush@kernel.org> wrote:
>
> On Fri, Oct 10 2025, Jason Miu wrote:
>
> > On Thu, Oct 9, 2025 at 9:19 PM Chris Li <chrisl@kernel.org> wrote:
> >>
> >> On Thu, Oct 9, 2025 at 4:21 PM Pratyush Yadav <pratyush@kernel.org> wrote:
> >> >
> >> > On Tue, Oct 07 2025, Chris Li wrote:
> >> >
> >> > [...]
> >> > > That will keep me busy for a while waiting for the VFIO series.
> >> >
> >> > I recall we talked in one of the biweekly meetings about some sanity
> >> > checking of folios right before reboot (make sure they are right order,
> >> > etc.) under a KEXEC_HANDOVER_DEBUG option. If you have some spare time
> >> > on your hands, would be cool to see some patches for that as well :-)
> >>
> >> Sure, I will add that to my "nice to have" list. No promised I got
> >> time to get to it with the PCI. It belong to the KHO series not PCI
> >> though.
> >>
>
> Right. It is only a "nice to have", and not a requirement. And certainly
> not for the PCI series.

Ack.


> >
> > For the folio sanity check with KEXEC_HANDOVER_DEBUG, I can follow
> > that up. Would you tell me what we like to check before reboot, I may
> > have missed some context. Thanks!
>
> The idea is to sanity-check the preserved folios in the kexec-reboot
> flow somewhere. The main check discussed was to make sure the folios are
> of the same order as they were preserved with. This will help catch bugs
> where folios might split after being preserved.

Yes, the idea is that, for all folio that has been preserved, remember
the folio order at the time of pserver_folio. Right before kexec
reboot, maybe after the freeze() call, the KHO can go though the
internal list of the preserved folio and verify the folio starting at
that physical address still has the same order compare to the
preservation time. In other words, the folio order hasn't change since
the between preserve_folio() and kexec reboot, for the folio that has
been preserved.

> Maybe we can add some more checks too? Like making sure the folios
> aren't freed after they were preserved. But that condition is a bit
> trickier to catch. But at least the former should be simple enough to
> do as a start.

Agree, we can have more check there. We can also add those additional
check as follow up patches in the same series or later series. They
don't have to be done in one go.

Chris