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Sat, 14 Mar 2026 18:06:30 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:f531:45b8:548c:e004] ([2a00:79e0:2eb0:8:f531:45b8:548c:e004]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82a07287ef8sm10728741b3a.29.2026.03.14.18.06.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Mar 2026 18:06:28 -0700 (PDT) Date: Sat, 14 Mar 2026 18:06:28 -0700 (PDT) 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 March 9, 2026 Message-ID: <2c094579-77d8-7de1-0a49-9138aeb69e84@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 15CC8C0006 X-Stat-Signature: 6itfes9fi9pka587wqb1t734z5pnc4s5 X-Rspam-User: X-HE-Tag: 1773536791-390447 X-HE-Meta: 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 mmLDZBLK 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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, March 9. 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----- Pasha updated on stateless KHO: it's now in Andrew's tree and ready to go for the next merge window. He noted that deferred struct page initialization was being worked on as a next step and then attention will shift to optimizing start up performance. We want to make sure KHO is not the long pole. Pratyush noted that there is a weird interaction between HVO, sparse init, and KHO. HugeTLB pages must be allocated before sparse init but when in KHO boot we are in scratch only which wouldn't allow for allocating such large amounts of memory. Pasha noted that there is an exception available where we can ensure that memory is coming from the preserved tree. Pratyush said we should parse the bitmaps and make the memblock reservations but we don't set the order in struct page, then turn off scratch and do the hugepage allocation and then parse the bitmap again to set the orders. ----->o----- We briefly talked about KHO enlightenment for ASI which wasn't deemed to be super urgent. ASI can be merged without KHO enlightenment so this could be a later extension. ----->o----- Pasha noted that he received some comments from Pratyush on the luod design[1] that he would be iterating through. We welcomed anybody else to continue to provide feedback as well directly on the doc. Pasha discussed with Jork and there will be a three-way meeting that will determine what the intercept will be with systemd. We discussed versioning support and when the timelines for landing the support would be. Pasha suggested that we would need this when we start making strong guarantees about supporting live update from version to version. Pratyush was working on HugeTLB preservation support ahead of this. ----->o----- Pratyush updated on HugeTLB preservation support and how it would be split into multiple parts. Part one is selftests that he sent out to the mailing list for review. He is currently blocked on the ordering issue mentioned above. Pratyush suggested upstream code review from upstream HugeTLB experts would be very useful on the list. We discussed handling this at the next Linux MM Alignment Session on Wednesday, March 18. ----->o----- David Matlack is prepping v3 of the VFIO support. He was working on preserving VFIO file descriptors but not preserving a lot of the device state itself. A question arose upstream about userspace being aware that we're in this development phase where files are preserved but not everything on the device is preserved. He didn't see a long-term need for a UAPI that expresses that it's saving bits and pieces of a device or letting userspace control what the kernel preserves and what it does not preseve. He was thinking of doing this under CONFIG_EXPERIMENTAL. ----->o----- Sami received some feedback for IOMMU persistence but otherwise no major updates. There were some patches sent from Intel that would be a small dependency for hitless replacement that Sami is looking at. ----->o----- Pasha brought up plans for the next steps for live update while keeping CPUs running through the reboot, which will be a long-term discussion. This will need to involve KVM folks in the upstream discussion. Jason said it would be very useful to demonstrate kexec live update with a very simple VM with no VFIO. David suggested a KVM selftest would be useful for this type of demo. ----->o----- Next meeting will be on Monday, March 23 at 8am PDT (UTC-7), everybody is welcome: https://meet.google.com/rjn-dmzu-hgq Topics for the next meeting: - luod design feedback and intersection with systemd; implementation and next steps - improving KHO and boot time performance, including deferred struct page initialization - HugeTLB preservation support including selftests + debrief discussion from Linux MM Alignment Session - 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 and patches from Intel - guest_memfd HugeTLB enlightenment: conversion support, HugeTLB support without restructuring, and HugeTLB support with restructuring - later: versioning support for luod to negotiate - later: ordering issues when disabling interrupts based on feedback from Nvidia - later: update on PCI preservation series and next steps - later: KHO enlightenment for ASI Please let me know if you'd like to propose additional topics for discussion, thank you! [1] https://tinyurl.com/luoddesign