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Sat, 28 Feb 2026 17:44:20 -0800 (PST) Received: from [2a00:79e0:2eb0:8:963e:838d:a96b:8016] ([2a00:79e0:2eb0:8:963e:838d:a96b:8016]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8273a01a9dasm9104749b3a.49.2026.02.28.17.44.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Feb 2026 17:44:19 -0800 (PST) Date: Sat, 28 Feb 2026 17:44:18 -0800 (PST) From: David Rientjes To: Alexander Graf , "Andersen, Tycho" , Anthony Yznaga , Baolu Lu , David Hildenbrand , David Matlack , James Gowans , Jason Gunthorpe , Mike Rapoport , Pankaj Gupta , Pasha Tatashin , Pratyush Yadav , Praveen Kumar , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" cc: linux-mm@kvack.org, kexec@lists.infradead.org Subject: [Hypervisor Live Update] Notes from February 23, 2026 Message-ID: <8dff046d-a819-ac8e-c1fa-8b5a35740cbb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Queue-Id: BE2B61C0007 X-Rspamd-Server: rspam08 X-Stat-Signature: nhkhjjtinim8xr53jbmdyeua6a7tray6 X-HE-Tag: 1772329462-741334 X-HE-Meta: U2FsdGVkX18LLOubkKSSuVRw5mKPPiJ3Xbx3IaOrTgWr8+syyidwg6AXwB8cYXEf7Y5g4bSBcXZR0UteciHSZz9LymiccOIfJbUEpUOnV+9OlOAzW0UltPPiCwtRiEqP6uBjt1DTrdd3BjEOLWElOR4IqakpOGnYLTtG4WY1P0QvBqlXk5ywdqLKnpiJI7FVGz4wHcOeQu0ZDEio3fa0Gyx95nIPiA9Qd9L7vV5pXZM2u62MN2JdKYYWwZwArkchp5YQqDlAulcrITsaFFPhGb3VVmQvgKXJBWoHgYVYisxejIcwHMCAG3y1YnkDqFcxTQNuWJ1vz1ohWteRJJpIHgCLgt02LAEJOEOCrY44Tanrb/R0PozEFIIVOFkey9ErhYp/5D/ATtmcwMOakOXH5ZonCwFzbV0vUPTaquTceZkAmojdVAhmamr4D9PqbUbuFbowGStNe18+5E7406QbUpJl6b6YBEqSFjIeLUV8XdEGolDVOsEMUeaDq3dxTPFErTyhHXI00g9V+hgO09Q2mm2Oyqn9AGqp6jRWeiYneRUS7uGe8/QOiSi+2yw2/kU604gn1pwffCBd6N+Y1W/44hMYJltGhUqKpxLmLRsmgVnt7QXX2yBBdDOGlfAY9uHDCPvoOIQHcghHa2DjhCy0Ro0lYjmqMRVqSRHMvTjGUDPcLDH8Ff3kGH8IoXoFVoVxDDq8Dt816OcsU0aqf1hPhncZV/RCwUhuYjoSmjuEcJpV6BM4f6FMLFX9x4nyuFJhSdaMKXWzkYwgcLr2GkrHZC5eow9qkCZM3gh1O4Y1Ws951Hi1jB15OI8hyfDCndaCSUEs7yg87rXbO+b44l1gWDTTXiG7sXulH1cZxcquBnKjj80Y/Hw8+F00WF7jDnwmhhBijfVviBknQFabF2JkAwfJkycy7y7/syrVlhyVJpb5QIzL1A+LuEpStYMAYaKb3VkWSAYuy0+lUsQt4xR XgG3/tkd 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi everybody, Here are the notes from the last Hypervisor Live Update call that happened on Monday, February 23. Thanks to everybody who was involved! These notes are intended to bring people up to speed who could not attend the call as well as keep the conversation going in between meetings. ----->o----- We briefly mentioned the luod design doc[1] and asked people for review, Pratyush noted that he would be taking a look at it. ----->o----- Jork Loeser noted that he was looking at HyperV partition survival. They donate pages to HyperV which is a concept that doesn't exist in KVM. These pages are removed from Linux entirely and cannot be accessed. He was playing with stateless KHO and extended some features but is not ready to send the patches out for review. He was wondering if there was a possibility of landing changes in 7.1. Pratyush noted that stateless KHO should go into the tree independently. Any consumers of the radix tree can be independent and build on top of those patches. He noted that he would be happy to review the patches when they come out. ----->o----- Pratyush noted that there were no updates for versioning support. There is a clear plan forward for it but it hasn't been implemented yet. He said he updated the HugeTLB preservation support with the requested changes from the mailing list but doesn't have selftests done yet. In two weeks, he was hoping that these would be posted to the list. ----->o----- David Matlack noted for interrupt ordering that discussions are still ongoing with NV on the topic. Right now the simple approach is being used for disabling interrupts on the device and then reenabling them after live update. For VFIO, there hasn't been a lot of feedback yet. He was going to ask Bjorn and Alex to take a look. ----->o----- Sami sent out phase 1 of the IOMMU preservation series and is looking forward to the next phase. He was asking people for review upstream. Sami is using the VFIO patch series as a dependency. ----->o----- Ackerley Tng went through guest_memfd HugeTLB support; the link to the slides are included in the cover letter for participants. He briefly touched on an introduction to guest_memfd as a guest-first memory provider to KVM. He then discussed how guest_memfd simply wraps existing sources of memory like pages from the buddy allocator or HugeTLB pages. The folios are put into the filemap. Every page is individually tracked to be either shared or private. Confidential guests can request a private page to be shared with the host and vice versa. For shared-to-private conversion, the userspace VMM makes sure that devices stop using the memory requested by checking refcounts and then sends the SET_MEMORY_ATTRIBUTES ioctl to guest_memfd; that unmaps the range from the userspace page tables and records the page as private before returning to the guest. Refcounting for a HugeTLB page is taken for the entire hugepage so we cannot identify which page within the hugepage the refcount was taken for. For all private-to-shared conversions this requires splitting hugepages into pages. Split folios have to be merged back together but may also out-live the guest_memfd; for example if the fd is closed the memory may finally be unpinned. This requires tracking outside of KVM such as the original size of the folio and which memcg was charged for it. This is also required for memory error handling. For KHO preservation, for guest_memfd pages (not HugeTLB pages) we need to preserve the filemap and associated folios, mempolicy, and memory attributes from the Maple Tree. For HugeTLB pages we must preserve the restructuring metadata. It was noted that there is no memory failure tracking today, it could be a future extension. Pratyush asked if we can disallow any conversions after prepare. Ackerley said if this period is very short than this should be fine. Pratyush also asked if we should associate the guest_memfd with the host VM which, today, we rely on the VMM to do. For timelines, Ackerley suggested that we would be able to merge conversion support with private/shared tracking in March and then HugeTLB support without restructuring in June. He was hoping to have restructuring support later this year. ----->o----- NOTE!! Daylight Savings Time starts on Sunday, March 8 so the time of the meeting may have changed for some participants. Next meeting will be on Monday, March 9 at 8am PDT (UTC-7), everybody is welcome: https://meet.google.com/rjn-dmzu-hgq Topics for the next meeting: - stateless KHO patch status in Andrew's tree - determine if luod would become part of systemd and discussions with Luca; implementation and next steps - versioning support for luod to negotiate - HugeTLB preservation support - ordering issues when disabling interrupts based on feedback from NV - VFIO patch series review from the list - phase 1 of IOMMU persistence patch series, then phase 2 status and updates - hitless replacement for iommu domains - guest_memfd HugeTLB enlightenment: conversion support, HugeTLB support without restructuring, and HugeTLB support with restructuring - live update related topics to propose for LSF/MM/BPF 2026 - KHO enlightenment for ASI - later: update on PCI preservation series and next steps - later: testing methodology to allow downstream consumers to qualify that live update works from one version to another - later: reducing blackout window during live update, including deferred struct page initialization Please let me know if you'd like to propose additional topics for discussion, thank you! [1] https://tinyurl.com/luoddesign