From: Jason Gunthorpe <jgg@nvidia.com>
To: Logan Odell <loganodell@google.com>
Cc: arnd@arndb.de, pasha.tatashin@soleen.com, rppt@kernel.org,
pratyush@kernel.org, graf@amazon.com, akpm@linux-foundation.org,
pbonzini@redhat.com, maz@kernel.org, oupton@kernel.org,
seanjc@google.com, bhelgaas@google.com, alex@shazbot.org,
kevin.tian@intel.com, dwmw2@infradead.org,
baolu.lu@linux.intel.com, joro@8bytes.org, will@kernel.org,
robin.murphy@arm.com, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
linux-mm@kvack.org, kvm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
linux-pci@vger.kernel.org, iommu@lists.linux.dev
Subject: Re: [RFC PATCH 0/3] liveupdate: Move to feature flags for LUO and memfd ABI compatibility
Date: Fri, 4 Sep 2026 13:00:09 -0300 [thread overview]
Message-ID: <20260904160009.GV4157646@nvidia.com> (raw)
In-Reply-To: <20260903023452.721732-1-loganodell@google.com>
On Wed, Sep 02, 2026 at 07:34:49PM -0700, Logan Odell wrote:
> We're including maintainers from all subsystems that currently is or
> will be expected to participate in live update to ensure alignment on
> the path forward for compatibility.
>
> Currently, Live Update Orchestrator (LUO) and its file handlers rely on
> monolithic compatibility strings (such as "luo-v5" and "memfd-v1") to
> validate ABI compatibility across kexec live updates. Any modification
> to serialized structures requires bumping the version string, which
> strictly breaks compatibility between adjacent kernels even when changes
> are additive, backwards-compatible, or optional.
That was the intention, I aruged strongly that upstream does not want
to maintain a CSP matrix of endless kernel version combinations. That
is far too much work to push on maintainers. Upstream would do much
less, maybe only same-version, depending.
> This RFC series transitions LUO and subsystem file handlers to use
> granular feature bitmasks instead of compatibility strings. We replace
> the compatibility string with a header structure that includes some
> reserved space to define the features that are included after the
> feature.
The compatability string is only a small part of it, you also need a
serializing ABI that can handle some random mixmash of these
features. Ie the various TLV schemes that were all proposed. What is
the plan here?
Jason
next prev parent reply other threads:[~2026-09-04 16:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 2:34 [RFC PATCH 0/3] liveupdate: Move to feature flags for LUO and memfd ABI compatibility Logan Odell
2026-09-03 2:34 ` [RFC PATCH 1/3] luo: Move to feature flags instead of compatibility strings Logan Odell
2026-09-03 2:34 ` [RFC PATCH 2/3] luo: Export feature support to vmlinux section Logan Odell
2026-09-03 2:34 ` [RFC PATCH 3/3] luo: memfd: Move to feature flags instead of compatibility strings Logan Odell
2026-09-04 16:00 ` Jason Gunthorpe [this message]
2026-09-04 22:24 ` [RFC PATCH 0/3] liveupdate: Move to feature flags for LUO and memfd ABI compatibility David Matlack
2026-09-05 1:24 ` Jason Gunthorpe
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