linux-stable.git/kernel/liveupdate/kexec_handover.c, branch linux-rolling-stable

kho: skip memoryless NUMA nodes when reserving scratch areas

2026-03-04T12:21:30+00:00

[ Upstream commit 427b2535f51342de3156babc6bdc3f3b7dd2c707 ]

kho_reserve_scratch() iterates over all online NUMA nodes to allocate
per-node scratch memory.  On systems with memoryless NUMA nodes (nodes
that have CPUs but no memory), memblock_alloc_range_nid() fails because
there is no memory available on that node.  This causes KHO initialization
to fail and kho_enable to be set to false.

Some ARM64 systems have NUMA topologies where certain nodes contain only
CPUs without any associated memory.  These configurations are valid and
should not prevent KHO from functioning.

Fix this by only counting nodes that have memory (N_MEMORY state) and skip
memoryless nodes in the per-node scratch allocation loop.

Link: https://lkml.kernel.org/r/20260120175913.34368-1-epetron@amazon.de
Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers").
Signed-off-by: Evangelos Petrongonas 
Reviewed-by: Pratyush Yadav 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pasha Tatashin 
Cc: Alexander Graf 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Sasha Levin

kho: kho_preserve_vmalloc(): don't return 0 when ENOMEM

2026-01-27T03:03:48+00:00

kho_preserve_vmalloc() should return -ENOMEM when new_vmalloc_chunk()
fails.

Reported-by: kernel test robot 
Reported-by: Dan Carpenter 
Closes: https://lore.kernel.org/r/202601211636.IRaejjdw-lkp@intel.com/
Reviewed-by: Pasha Tatashin 
Reviewed-by: Pratyush Yadav 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Alexander Graf 
Cc: Jason Gunthorpe 
Cc: Pasha Tatashin 
Signed-off-by: Andrew Morton

kho: init alloc tags when restoring pages from reserved memory

2026-01-27T03:03:47+00:00

Memblock pages (including reserved memory) should have their allocation
tags initialized to CODETAG_EMPTY via clear_page_tag_ref() before being
released to the page allocator.  When kho restores pages through
kho_restore_page(), missing this call causes mismatched
allocation/deallocation tracking and below warning message:

alloc_tag was not set
WARNING: include/linux/alloc_tag.h:164 at ___free_pages+0xb8/0x260, CPU#1: swapper/0/1
RIP: 0010:___free_pages+0xb8/0x260
 kho_restore_vmalloc+0x187/0x2e0
 kho_test_init+0x3c4/0xa30
 do_one_initcall+0x62/0x2b0
 kernel_init_freeable+0x25b/0x480
 kernel_init+0x1a/0x1c0
 ret_from_fork+0x2d1/0x360

Add missing clear_page_tag_ref() annotation in kho_restore_page() to
fix this.

Link: https://lkml.kernel.org/r/20260122132740.176468-1-ranxiaokai627@163.com
Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation")
Signed-off-by: Ran Xiaokai 
Reviewed-by: Pratyush Yadav 
Reviewed-by: Pasha Tatashin 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Alexander Graf 
Cc: Kent Overstreet 
Cc: Suren Baghdasaryan 
Cc: 
Signed-off-by: Andrew Morton

kho: validate preserved memory map during population

2026-01-15T06:16:21+00:00

If the previous kernel enabled KHO but did not call kho_finalize() (e.g.,
CONFIG_LIVEUPDATE=n or userspace skipped the finalization step), the
'preserved-memory-map' property in the FDT remains empty/zero.

Previously, kho_populate() would succeed regardless of the memory map's
state, reserving the incoming scratch regions in memblock.  However,
kho_memory_init() would later fail to deserialize the empty map.  By that
time, the scratch regions were already registered, leading to partial
initialization and subsequent list corruption (freeing scratch area twice)
during kho_init().

Move the validation of the preserved memory map earlier into
kho_populate(). If the memory map is empty/NULL:
1. Abort kho_populate() immediately with -ENOENT.
2. Do not register or reserve the incoming scratch memory, allowing the new
   kernel to reclaim those pages as standard free memory.
3. Leave the global 'kho_in' state uninitialized.

Consequently, kho_memory_init() sees no active KHO context
(kho_in.mem_chunks_phys is 0) and falls back to kho_reserve_scratch(),
allocating fresh scratch memory as if it were a standard cold boot.

Link: https://lkml.kernel.org/r/20251223140140.2090337-1-pasha.tatashin@soleen.com
Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
Signed-off-by: Pasha Tatashin 
Reported-by: Ricardo Neri 
Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
Reviewed-by: Mike Rapoport (Microsoft) 
Tested-by: Ricardo Neri 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Signed-off-by: Andrew Morton

kho: fix restoring of contiguous ranges of order-0 pages

2025-11-27T22:24:44+00:00

When contiguous ranges of order-0 pages are restored, kho_restore_page()
calls prep_compound_page() with the first page in the range and order as
parameters and then kho_restore_pages() calls split_page() to make sure
all pages in the range are order-0.

However, since split_page() is not intended to split compound pages and
with VM_DEBUG enabled it will trigger a VM_BUG_ON_PAGE().

Update kho_restore_page() so that it will use prep_compound_page() when it
restores a folio and make sure it properly sets page count for both large
folios and ranges of order-0 pages.

Link: https://lkml.kernel.org/r/20251125110917.843744-3-rppt@kernel.org
Fixes: a667300bd53f ("kho: add support for preserving vmalloc allocations")
Signed-off-by: Mike Rapoport (Microsoft) 
Reported-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Pasha Tatashin 
Signed-off-by: Andrew Morton

kho: kho_restore_vmalloc: fix initialization of pages array

2025-11-27T22:24:44+00:00

Patch series "kho: fixes for vmalloc restoration".

Pratyush reported off-list that when kho_restore_vmalloc() is used to
restore a vmalloc_huge() allocation it hits VM_BUG_ON() when we
reconstruct the struct pages in kho_restore_pages().

These patches fix the issue.


This patch (of 2):

In case a preserved vmalloc allocation was using huge pages, all pages in
the array of pages added to vm_struct during kho_restore_vmalloc() are
wrongly set to the same page.

Fix the indexing when assigning pages to that array.

Link: https://lkml.kernel.org/r/20251125110917.843744-1-rppt@kernel.org
Link: https://lkml.kernel.org/r/20251125110917.843744-2-rppt@kernel.org
Fixes: a667300bd53f ("kho: add support for preserving vmalloc allocations")
Signed-off-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Pasha Tatashin 
Signed-off-by: Andrew Morton

KHO: fix boot failure due to kmemleak access to non-PRESENT pages

2025-11-27T22:24:43+00:00

When booting with debug_pagealloc=on while having:
CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n
the system fails to boot due to page faults during kmemleak scanning.

This occurs because:
With debug_pagealloc is enabled, __free_pages() invokes
debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for freed
pages in the kernel page table.  KHO scratch areas are allocated from
memblock and noted by kmemleak.  But these areas don't remain reserved but
released later to the page allocator using init_cma_reserved_pageblock(). 
This causes subsequent kmemleak scans access non-PRESENT pages, leading to
fatal page faults.

Mark scratch areas with kmemleak_ignore_phys() after they are allocated
from memblock to exclude them from kmemleak scanning before they are
released to buddy allocator to fix this.

[ran.xiaokai@zte.com.cn: add comment]
  Link: https://lkml.kernel.org/r/20251127122700.103927-1-ranxiaokai627@163.com
Link: https://lkml.kernel.org/r/20251122182929.92634-1-ranxiaokai627@163.com
Signed-off-by: Ran Xiaokai 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Catalin Marinas 
Cc: Changyuan Lyu 
Cc: Pasha Tatashin 
Signed-off-by: Andrew Morton

kho: free chunks using free_page() instead of kfree()

2025-11-27T22:24:42+00:00

Before commit fa759cd75bce5 ("kho: allocate metadata directly from the
buddy allocator"), the chunks were allocated from the slab allocator using
kzalloc().  Those were rightly freed using kfree().

When the commit switched to using the buddy allocator directly, it missed
updating kho_mem_ser_free() to use free_page() instead of kfree().

Link: https://lkml.kernel.org/r/20251118182218.63044-1-pratyush@kernel.org
Fixes: fa759cd75bce5 ("kho: allocate metadata directly from the buddy allocator")
Signed-off-by: Pratyush Yadav 
Reviewed-by: Pasha Tatashin 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Alexander Graf 
Cc: David Matlack 
Signed-off-by: Andrew Morton

kho: add Kconfig option to enable KHO by default

2025-11-27T22:24:37+00:00

Currently, Kexec Handover must be explicitly enabled via the kernel
command line parameter `kho=on`.

For workloads that rely on KHO as a foundational requirement (such as the
upcoming Live Update Orchestrator), requiring an explicit boot parameter
adds redundant configuration steps.

Introduce CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT.  When selected, KHO
defaults to enabled.  This is equivalent to passing kho=on at boot.  The
behavior can still be disabled at runtime by passing kho=off.

Link: https://lkml.kernel.org/r/20251114190002.3311679-14-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Arnd Bergmann 
Cc: Baoquan He 
Cc: Coiby Xu 
Cc: Dave Vasilevsky 
Cc: Eric Biggers 
Cc: Kees Cook 
Signed-off-by: Andrew Morton

kho: allow memory preservation state updates after finalization

2025-11-27T22:24:36+00:00

Currently, kho_preserve_* and kho_unpreserve_* return -EBUSY if KHO is
finalized.  This enforces a rigid "freeze" on the KHO memory state.

With the introduction of re-entrant finalization, this restriction is no
longer necessary.  Users should be allowed to modify the preservation set
(e.g., adding new pages or freeing old ones) even after an initial
finalization.

The intended workflow for updates is now:
1. Modify state (preserve/unpreserve).
2. Call kho_finalize() again to refresh the serialized metadata.

Remove the kho_out.finalized checks to enable this dynamic behavior.

This also allows to convert kho_unpreserve_* functions to void, as they do
not return any error anymore.

Link: https://lkml.kernel.org/r/20251114190002.3311679-13-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Arnd Bergmann 
Cc: Baoquan He 
Cc: Coiby Xu 
Cc: Dave Vasilevsky 
Cc: Eric Biggers 
Cc: Kees Cook 
Signed-off-by: Andrew Morton