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Sat, 11 Apr 2026 17:14:23 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:3927:c82:6a08:f01a] ([2a00:79e0:2eb0:8:3927:c82:6a08:f01a]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b2d4dd7faasm70316735ad.26.2026.04.11.17.14.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 11 Apr 2026 17:14:22 -0700 (PDT) Date: Sat, 11 Apr 2026 17:14:21 -0700 (PDT) From: David Rientjes To: Alexander Graf , "Andersen, Tycho" , Anthony Yznaga , Baolu Lu , David Hildenbrand , David Matlack , "Heyne, Maximillian" , 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 April 6, 2026 Message-ID: <82db97e1-791b-770a-ebea-0e364dbd08d7@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260411_171425_953613_D0EE8799 X-CRM114-Status: GOOD ( 27.86 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org Hi everybody, Here are the notes from the last Hypervisor Live Update call that happened on Monday, April 6. 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 noted that discussions happened between Luca, Jork, and Pratyush for LUO integration into systemd. Luca had written a first attempt at integration and it required some changes for LUO. It was also discussed that unit files that start the VMMs will include the session name in the unit file itself so at shutdown, systemd will know the sessions that are created. There was no update on the timeline for this work, however, the next step was to start discussions with other systemd maintainers. There was no update on the status of boot time performance optimizations like deferred struct page initialization. ----->o----- Pratyush had no updates for HugeTLB preservation after being out of office; he thinks that the memfd selftest series is close to landing upstream, however. He also updated offline that KHO patches to lift the limit on the maximum preservation order from folios has been in the mm tree for a while and should ideally land in the next merge window. This work is a prerequisite for the HugeTLB preservation extension. Pratyush is also working on a fallback allocation strategy for KHO when scratch runs out. When walking the preservation bit maps, the goal is to find a big gap to fulfill the allocation; he had an initial patch series that works and is still iterating on it internally. This is also going to be a prerequisite for HugeTLB preservation. I provided the link to the Linux MM Alignment Session that was had on these HugeTLB topics if people were interested in watching the video. Pasha noted that the biggest takeaway from that session was the CMA limitation and supporting early boot HVO because KHO requires a struct page for every page that is being preserved early in boot, and this turns out to be incompatible with HVO. These would need to be resolved to be fully compatible with upstream support. ----->o----- David Matlack updated on VFIO v3 which was getting feedback upstream especially on PCI. v4 will split this series into two with David posting the first series (PCI) and Vipin Sharma posting the second series (VFIO and selftests). This will allow for faster iteration. Pasha asked if the PCI changes are likely to be able to stay within the PCI subsystem itself or will it have broader scope. David did not think we would need to change anything in struct device. Pasha asked about the scenario where a host driver needs to be preserved, David said this would still be the struct for PCI device on top of the struct device driver; he was optimistic we would be able to come up with changes in PCI core without becoming overly broad. The group wanted to fork off a separate discussion on non-FD related PCI drivers and how to support them in a generic way. ----->o----- Samiullah updated on the status of the IOMMU persistence patch series, he was planning on the next series to be posted over the next week or week and a half. ----->o----- Ackerley also updated on the status of guest_memfd HugeTLB support and indicated he was still working on the conversion support. He suggested there will be an update over the next two weeks and was targeting final reviews by the end of April. Pasha asked about current limitations in Ackerley's series, what features are needed as follow-up after his work is going to be done. Vishal noted that there may be some memory error handling that would need to be extended. Other than that, it was targeting full parity with HugeTLB. Vishal noted that direct map removal was under discussion upstream to support CVM use cases. ----->o----- Vishal noted that Sagi was starting to look at KHO support for CVMs. Vishal asked about KVM page tables and the memory donated to the TDX module and, in the future, will also be used for ARM CC. He asked for example of preservation of kernel owned memory. David Matlack noted that IOMMU preserves page tables so we could look at Samiullah's patches. Pasha noted that if memory is going to be preserved then it has to be pinned. The consensus of the group was to get started with guest_memfd preservation and then to add support for CVM use cases on top of that. ----->o----- Next meeting will be on Monday, April 20 at 8am PDT (UTC-7), everybody is welcome: https://meet.google.com/rjn-dmzu-hgq Topics for the next meeting: - systemd integration for LUO, socializing the design ideas with other systemd maintainers - any progress for KHO optimizations for boot time performance including initialization of memblock list and deferred struct page initialization - HugeTLB preservation support including selftests and fallback allocation strategy - VFIO v4 patch series status, separated between PCI and VFIO+selftests - IOMMU persistence patch series status - Maximillian: supporting CRIU with KHO by using memfd to store the state of a process, moving mmemory from a process to memfd - guest_memfd HugeTLB enlightenment: conversion support, HugeTLB support without restructuring, and HugeTLB support with restructuring - KHO support for Confidential VMs including page table preservation and pinning - later: versioning support for luod to negotiate - later: KHO enlightenment for ASI Please let me know if you'd like to propose additional topics for discussion, thank you!