When Linux runs as an L1 Virtual Host (L1VH) under Hyper-V, the MSHV root partition driver deposits pages to the hypervisor and creates partitions for guest VMs. Prior patches enabled kexec for L1VH, but only when no partitions had been created and no memory had been donated.
This series lifts that limitation. It uses KHO (Kexec Handover) to: - Track all pages deposited to the hypervisor in a KHO radix tree and preserve them across kexec so the new kernel knows which pages are owned by the hypervisor. - Freeze running partitions before kexec, record their IDs in the KHO FDT, and vacuum (tear down + reclaim memory) stale partitions after kexec. - In case of a crash, exclude hypervisor-owned pages from crash dump collection by passing the radix tree root PA via Hyper-V crash MSR P2 to the crash kernel. Dependency on Pratyush's KHO series =================================== Patches 1-12 are cherry-picked from Pratyush Yadav's v1 series "kho: make boot time huge page allocation work nicely with KHO" [1], which is still under discussion. This series uses functionality from those patches -- specifically the meta-data page enumeration via table callbacks and the restructured radix tree API. It also extends the KHO radix tree with: - A freeze mechanism to lock the tree before serializing for kexec (patch 13). - A crash-kernel-safe variant that memremaps radix nodes for use outside the direct map (patch 14). Patch overview ============== Patches 1-12: KHO radix tree and memblock changes (from [1]) Patch 13: Radix tree freeze and del_key() error reporting Patch 14: Crash-kernel-safe radix tree presence check Patch 15: Page tracker using KHO radix tree for deposited pages Patch 16: Debugfs interface for page tracker Patches 17-18: Crash MSR reshuffling + crash dump page exclusion Patch 19: Export kexec_in_progress for modules Patch 20: Freeze and vacuum partitions across kexec Feedback ======== This is an RFC. I am looking for feedback on the overall approach as well as the KHO changes (patches 13-14). [1] https://lore.kernel.org/linux-mm/[email protected]/ Based-on: linux-next/master (next-20260527) Jork Loeser (8): kho: add radix tree freeze and del_key() error reporting kho: Add crash-kernel-safe radix tree presence check mshv: Use page tracker to manage MSHV-owned pages and preserve with KHO mshv: Add debugfs interface to page tracker hyperv: Reserve crash MSR P2 for page preservation root PA mshv: Exclude Hyper-V donated pages from crash dump collection kexec: export kexec_in_progress for modules mshv: freeze and vacuum partitions across kexec Pratyush Yadav (Google) (12): kho: generalize radix tree APIs kho: store incoming radix tree in kho_in kho: add a struct for radix callbacks kho: add callback for table pages kho: add data argument to radix walk callback kho: allow early-boot usage of the KHO radix tree kho: allow destroying KHO radix tree kho: add kho_radix_init_tree() memblock: introduce MEMBLOCK_KHO_SCRATCH_EXT kho: extended scratch kho: return virtual address of mem_map mm/hugetlb: make bootmem allocation work with KHO arch/arm64/hyperv/hv_core.c | 6 +- arch/x86/hyperv/hv_init.c | 4 +- drivers/hv/Kconfig | 3 + drivers/hv/Makefile | 2 +- drivers/hv/hv_common.c | 5 +- drivers/hv/hv_proc.c | 32 +- drivers/hv/mshv_debugfs.c | 99 +++++ drivers/hv/mshv_page_preserve.c | 557 ++++++++++++++++++++++++++ drivers/hv/mshv_page_preserve.h | 21 + drivers/hv/mshv_root.h | 5 + drivers/hv/mshv_root_hv_call.c | 12 +- drivers/hv/mshv_root_main.c | 341 ++++++++++++++-- include/linux/kexec_handover.h | 1 + include/linux/kho_radix_tree.h | 90 ++++- include/linux/memblock.h | 14 + kernel/kexec_core.c | 1 + kernel/liveupdate/kexec_handover.c | 605 +++++++++++++++++++++++------ mm/hugetlb.c | 19 +- mm/memblock.c | 177 +++++++-- mm/mm_init.c | 1 + 20 files changed, 1767 insertions(+), 228 deletions(-) create mode 100644 drivers/hv/mshv_page_preserve.c create mode 100644 drivers/hv/mshv_page_preserve.h -- 2.43.0
