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Mon, 03 Aug 2026 16:31:06 +0800 Date: Mon, 3 Aug 2026 16:30:56 +0800 From: Chenghao Duan To: Pasha Tatashin Cc: Alexander Graf , "Andersen, Tycho" , Anthony Yznaga , Baolu Lu , David Hildenbrand , David Matlack , "Heyne, Maximillian" , James Gowans , Jason Gunthorpe , Mike Rapoport , Pankaj Gupta , Pratyush Yadav , Praveen Kumar , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" , Luca Boccassi , Samiullah Khawaja , Jork Loeser , Zhu Yanjun , linux-mm@kvack.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [Hypervisor Live Update] Notes from July 27, 2026 Message-ID: <20260803082957.GA861524@chenghao-pc> References: <20260801123213.2259109-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260801123213.2259109-1-pasha.tatashin@soleen.com> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DD7B31C0010 X-Stat-Signature: 5zf9pz3oitknikps5xfubojfmbqaox4d X-HE-Tag: 1785745882-237461 X-HE-Meta: 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 1XcnuIpb QuYhXj9jDlL3DxlUAy+jzJFiPDLkO6qoUeRrdgV4kKa5dukfQFghDkn5BKNlGEL+iwRd92Rqg3WSxwJ7jfI7L8yaoai9fwQ+apqTeJPMDRDwj85YanzVOafQ+L+OFJ5VaMjaY72ERBGBIRCPkKh7hCDeKrY5S6mzhk1HT727FlIJD570wpQBhO+6coji+a6Pa/Yv41prGl24EkNqbsFI1YiX2UyZydidxtFvzWJxCDNtrVnGqLvmK9jUIaQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Aug 01, 2026 at 08:32:07AM -0400, Pasha Tatashin wrote: > Hi everybody, > > Here are the notes from our Hypervisor Live Update call held on July 27. > These notes are intended to bring those who could not attend up to speed > and to keep the momentum going between meetings. > > ----->o----- > LPC 2026 Call for Proposals & Registration > > * Deadline Extension: The Call for Proposals deadline for all LPC 2026 > microconferences in Prague has been extended to August 7th. > > https://lore.kernel.org/all/ahcc3Qyuy7Oy03Iq@plex > > * KVM Track Load Balancing: Due to a strong number of proposals for the > Live Update Microconference, the team discussed moving select topics > to the KVM track to balance the schedule. Orphaned VM topics (proposed > by Pasha and Pratyush) and potentially guest_memfd preservation will > be submitted to both tracks. Pratyush will coordinate with organizers > of both tracks to ensure talks are accepted in one track rather than > duplicated. > > ----->o----- > PCIe Persistence > > * PCI v8 Status: David Matlack is preparing the v8 PCI series, targeting > submission by Tuesday/Wednesday before leaving for vacation. > > * Versioning in Structure: Versioning is being moved out of the compatibility > string (which will remain a constant string like "pci") and into the first > field of the pci_ser structure. Because retrieve failures in the PCI core > are fatal and require a kernel panic to prevent memory corruption in > dependent subsystems (such as IOMMU), embedding the version in the struct > allows the kernel to reliably distinguish between missing FLB data and an > incompatible version. > > * Reviews & Landing Strategy: Bjorn Helgaas provided review comments and > Reviewed-by tags on several patches, including feedback on structuring > and naming for the bus number preservation patch. David will reply to the > v7 cover letter to propose merging the initial series through the Live > Update tree due to dependencies in liveupdate/next. > > ----->o----- > VFIO Persistence > > * VFIO v5/v6 Status: Vipin Sharma sent out VFIO v5 on July 14th and is > working on v6 to address review comments, targeting submission in 2-3 > weeks. > > * Lockdep Investigation: A lockdep warning reported during testing was > investigated and determined to be unrelated to Live Update (involving CPU > hotplug locks during boot group operations and ATS). Vipin will start a > separate mailing list thread with a reproducer to discuss the lockdep > issue independently so it does not block the VFIO series. > > * Landing Strategy: Vipin requested guidance on the base tree for landing > initial VFIO patches. Pasha will reply on the cover letter thread to > initiate discussion with Alex Williamson and maintainers. > > ----->o----- > IOMMU Persistence > > * IOMMU v4 Status: Samiullah Khawaja plans to post v4 this week. Changes > include lifecycle edge-case fixes identified by Sashiko, refactoring to > separate non-live-update functions, and adopting the constant compatibility > string with private struct versioning (matching PCI v8). > > * Recoverable Error Retry Logic: Samiullah noted that retry logic for > recoverable errors is not required for Phase 1 and will be deferred until > needed by subsequent patch series. > > * Dependency Ordering Documentation: In response to Pratyush's question > regarding file preservation ordering, Pasha and Samiullah reaffirmed that > LUO does not enforce a hardcoded preservation sequence. Any ordering > restrictions imposed by file handlers (e.g., preserving during preserve > rather than freeze) are strictly for optimization or immutability reasons. > Samiullah will explicitly document these guidelines in-tree. Future > evolution may only relax ordering requirements, never make them stricter. > > ----->o----- > KHO & LUO > > * KHO Scratch Extension v4: Pratyush Yadav posted v4 of the KHO scratch > extension series on Friday. Feedback from Sashiko was primarily on > pre-existing issues; Pratyush aims to land the series in the current > merge window. > > * LoongArch KHO Support: Pratyush followed up with the LoongArch developer > regarding boot protocol preferences and maintainer feedback; awaiting > further updates. > > ----->o----- > Guest Memory (guest_memfd) & HugeTLB > > * guest_memfd v4 Status: Tarun Sahu is ready with v4 and plans to post it > this week. The update integrates negative tests, including verifying > allocation failures when guest_memfd is frozen during preservation and > ensuring guest_memfd without required flags is not preserved. > > * IOMMU Interaction & Freezing: The group discussed how IOMMU DMA pinning > interacts with shared guest_memfd preservation. Unlike regular shmem/mmfd > where sealing prevents hole-punching (fallocate), guest_memfd currently > relies on freezing during preservation. The team agreed on a phased > approach: > 1. Proceed with the current guest_memfd v4 series as-is (using freezing), > with a cover letter note clarifying that IOMMU support for guest_memfd > will be addressed in a later phase. > 2. Pratyush will explore removing the freezing requirement for mmfd and > guest_memfd in favor of dynamic updates to serialization structures. > 3. Implement IOMMU support for guest_memfd once the freezing/updating > model is finalized. > > * HugeTLB: On hold pending landing of the extended scratch memory series > and removal of freezing. > > ----->o----- > Orphaned VMs & Development Environment > > * Prototype & Repository: Pasha presented an update and demo on Orphaned VMs > (allowing VMs to survive host kexec/reboot without stopping vCPUs). He > published an open-source development environment repository: What are all the features mentioned above? Are user-space out-of-kernel tools included in scope? > > https://github.com/soleen/orphanvm I cannot access this URL, as it returns a 404 error. BRs Chenghao > > * NanoVM & Simics: The repository includes a lightweight C-based VMM > (nanovm) that demonstrates end-to-end live update across kexec. Pasha is > running it under Simics, which provides full hardware emulation of Intel > VTX virtualization instructions (unlike QEMU full emulation), booting the > host VM in ~6 seconds and nested guest VM in ~5 seconds (real time). This > provides a clean, bare-metal-like environment to study vCPU state and VM > exits during reboot. > > ----->o----- > Action Items & Next Steps > > Pasha: > * Reply on the VFIO cover letter thread regarding the landing tree strategy > with maintainers. > * Coordinate with LPC KVM and Live Update microconference organizers regarding > track placement for Orphaned VM and guest_memfd topics. > > David M: > * Post PCI v8 series. > * Reply to the PCI v7 cover letter proposing merging the initial series > through the Live Update tree. > > Vipin: > * Start a separate mailing list thread with a reproducer for the lockdep > issue independent of the VFIO live update series. > * Continue work on VFIO v6. > > Samiullah: > * Post IOMMU v4 series. > * Document in-tree guidelines for file preservation ordering dependencies > and optimization/immutability requirements. > > Pratyush: > * Follow up with LoongArch maintainers regarding KHO boot protocol support. > * Submit LPC talk proposal to the KVM track and coordinate with organizers. > * Continue work on removing freezing requirements for shmem/guest_memfd. > > Tarun: > * Post guest_memfd preservation v4 (including cover letter note regarding > future IOMMU support). > > ----->o----- > > Next meeting will be on Monday, August 10 at 8am PDT (UTC-7), everybody is > welcome! > > Join Here: https://meet.google.com/rjn-dmzu-hgq > > Please let me know if you'd like to propose additional topics for > discussion, thank you! > > Best regards, > Pasha