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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 Message-ID: <20260904160009.GV4157646@nvidia.com> References: <20260903023452.721732-1-loganodell@google.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260903023452.721732-1-loganodell@google.com> X-ClientProxiedBy: YT3PR01CA0126.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:83::22) To 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wXlRDvKjL4+sjLU3UmgoCYFBG9Ty50W6ljNxiHjfugquIksTinRDYnUPYkDobE+utEw2TgBGH/gUY1uKYovq9FlBMBos5n12ehRNaHq6QkLcL1S+2jaSDpQM8QweHbi5QLsFWhzgKt99ToLyFDIANltjKgcugrkobxHEQiEMn0gY4IaAbg9NvsZJz68QL/RKnlWRuODxAoL/IcMgnm4HFP/oJaSzcCxV06tw28kTitiHN8X71IL/3Ic6ciisv5XY54CK+e8pjogjQyfDiOQ2NSzcsJPrFbaa7ivwpSN/1izx/5CkrVb5XsttxFgS35e8MVyoJiFlSjxirSRsEOxxrHtvCXInY99VQCO50waLmg5R+wB8ygSvMKC6Z2+MeHOhD2j38ym9lLmJoQmmWiM9K6j0gRA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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