Re: [PATCH v4 00/30] Live Update Orchestrator

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Oct 09, 2025 at 02:37:44PM -0400, Pasha Tatashin wrote:
> On Thu, Oct 9, 2025 at 1:39 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
> >
> > On Thu, Oct 09, 2025 at 11:01:25AM -0400, Pasha Tatashin wrote:
> > > In this case we can enforce strict
> > > ordering during retrieval. If "struct file" can be retrieved by
> > > anything within the kernel, then that could be any kernel process
> > > during boot, meaning that charging is not going to be properly applied
> > > when kernel allocations are performed.
> >
> > Ugh, yeah, OK that's irritating and might burn us, but we did decide
> > on that strategy.
> >
> > > > I would argue it should always cause a preservation...
> > > >
> > > > But this is still backwards, what we need is something like
> > > >
> > > > liveupdate_preserve_file(session, file, &token);
> > > > my_preserve_blob.file_token = token
> > >
> > > We cannot do that, the user should have already preserved that file
> > > and provided us with a token to use, if that file was not preserved by
> > > the user it is a bug. With this proposal, we would have to generate a
> > > token, and it was argued that the kernel should not do that.
> >
> > The token is the label used as ABI across the kexec. Each entity doing
> > a serialization can operate it's labels however it needs.
> >
> > Here I am suggeting that when a kernel entity goes to record a struct
> > file in a kernel ABI structure it can get a kernel generated token for
> > it.
> 
> Sure, we can consider allowing the kernel to preserve dependent FDs
> automatically in the future, but is there a compelling use case that
> requires it right now?

Right now for the three prototype series.. Hmm, yes, I think we can
avoid implementing this.

In the future I suspect iommufd will need to restore the KVM fd since
stuff in the KVM sometimes becomes entangled with the iommu in some
cases on some arches.

The issue here is not order, it is straight up 'what value does
iommufd write to it's kexec ABI struct to refer to the KVM fd'.

Jason