Merge tag 'mm-stable-2025-05-31-14-50' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - "Add folio_mk_pte()" from Matthew Wilcox simplifies the act of
   creating a pte which addresses the first page in a folio and reduces
   the amount of plumbing which architecture must implement to provide
   this.

 - "Misc folio patches for 6.16" from Matthew Wilcox is a shower of
   largely unrelated folio infrastructure changes which clean things up
   and better prepare us for future work.

 - "memory,x86,acpi: hotplug memory alignment advisement" from Gregory
   Price adds early-init code to prevent x86 from leaving physical
   memory unused when physical address regions are not aligned to memory
   block size.

 - "mm/compaction: allow more aggressive proactive compaction" from
   Michal Clapinski provides some tuning of the (sadly, hard-coded (more
   sadly, not auto-tuned)) thresholds for our invokation of proactive
   compaction. In a simple test case, the reduction of a guest VM's
   memory consumption was dramatic.

 - "Minor cleanups and improvements to swap freeing code" from Kemeng
   Shi provides some code cleaups and a small efficiency improvement to
   this part of our swap handling code.

 - "ptrace: introduce PTRACE_SET_SYSCALL_INFO API" from Dmitry Levin
   adds the ability for a ptracer to modify syscalls arguments. At this
   time we can alter only "system call information that are used by
   strace system call tampering, namely, syscall number, syscall
   arguments, and syscall return value.

   This series should have been incorporated into mm.git's "non-MM"
   branch, but I goofed.

 - "fs/proc: extend the PAGEMAP_SCAN ioctl to report guard regions" from
   Andrei Vagin extends the info returned by the PAGEMAP_SCAN ioctl
   against /proc/pid/pagemap. This permits CRIU to more efficiently get
   at the info about guard regions.

 - "Fix parameter passed to page_mapcount_is_type()" from Gavin Shan
   implements that fix. No runtime effect is expected because
   validate_page_before_insert() happens to fix up this error.

 - "kernel/events/uprobes: uprobe_write_opcode() rewrite" from David
   Hildenbrand basically brings uprobe text poking into the current
   decade. Remove a bunch of hand-rolled implementation in favor of
   using more current facilities.

 - "mm/ptdump: Drop assumption that pxd_val() is u64" from Anshuman
   Khandual provides enhancements and generalizations to the pte dumping
   code. This might be needed when 128-bit Page Table Descriptors are
   enabled for ARM.

 - "Always call constructor for kernel page tables" from Kevin Brodsky
   ensures that the ctor/dtor is always called for kernel pgtables, as
   it already is for user pgtables.

   This permits the addition of more functionality such as "insert hooks
   to protect page tables". This change does result in various
   architectures performing unnecesary work, but this is fixed up where
   it is anticipated to occur.

 - "Rust support for mm_struct, vm_area_struct, and mmap" from Alice
   Ryhl adds plumbing to permit Rust access to core MM structures.

 - "fix incorrectly disallowed anonymous VMA merges" from Lorenzo
   Stoakes takes advantage of some VMA merging opportunities which we've
   been missing for 15 years.

 - "mm/madvise: batch tlb flushes for MADV_DONTNEED and MADV_FREE" from
   SeongJae Park optimizes process_madvise()'s TLB flushing.

   Instead of flushing each address range in the provided iovec, we
   batch the flushing across all the iovec entries. The syscall's cost
   was approximately halved with a microbenchmark which was designed to
   load this particular operation.

 - "Track node vacancy to reduce worst case allocation counts" from
   Sidhartha Kumar makes the maple tree smarter about its node
   preallocation.

   stress-ng mmap performance increased by single-digit percentages and
   the amount of unnecessarily preallocated memory was dramaticelly
   reduced.

 - "mm/gup: Minor fix, cleanup and improvements" from Baoquan He removes
   a few unnecessary things which Baoquan noted when reading the code.

 - ""Enhance sysfs handling for memory hotplug in weighted interleave"
   from Rakie Kim "enhances the weighted interleave policy in the memory
   management subsystem by improving sysfs handling, fixing memory
   leaks, and introducing dynamic sysfs updates for memory hotplug
   support". Fixes things on error paths which we are unlikely to hit.

 - "mm/damon: auto-tune DAMOS for NUMA setups including tiered memory"
   from SeongJae Park introduces new DAMOS quota goal metrics which
   eliminate the manual tuning which is required when utilizing DAMON
   for memory tiering.

 - "mm/vmalloc.c: code cleanup and improvements" from Baoquan He
   provides cleanups and small efficiency improvements which Baoquan
   found via code inspection.

 - "vmscan: enforce mems_effective during demotion" from Gregory Price
   changes reclaim to respect cpuset.mems_effective during demotion when
   possible. because presently, reclaim explicitly ignores
   cpuset.mems_effective when demoting, which may cause the cpuset
   settings to violated.

   This is useful for isolating workloads on a multi-tenant system from
   certain classes of memory more consistently.

 - "Clean up split_huge_pmd_locked() and remove unnecessary folio
   pointers" from Gavin Guo provides minor cleanups and efficiency gains
   in in the huge page splitting and migrating code.

 - "Use kmem_cache for memcg alloc" from Huan Yang creates a slab cache
   for `struct mem_cgroup', yielding improved memory utilization.

 - "add max arg to swappiness in memory.reclaim and lru_gen" from
   Zhongkun He adds a new "max" argument to the "swappiness=" argument
   for memory.reclaim MGLRU's lru_gen.

   This directs proactive reclaim to reclaim from only anon folios
   rather than file-backed folios.

 - "kexec: introduce Kexec HandOver (KHO)" from Mike Rapoport is the
   first step on the path to permitting the kernel to maintain existing
   VMs while replacing the host kernel via file-based kexec. At this
   time only memblock's reserve_mem is preserved.

 - "mm: Introduce for_each_valid_pfn()" from David Woodhouse provides
   and uses a smarter way of looping over a pfn range. By skipping
   ranges of invalid pfns.

 - "sched/numa: Skip VMA scanning on memory pinned to one NUMA node via
   cpuset.mems" from Libo Chen removes a lot of pointless VMA scanning
   when a task is pinned a single NUMA mode.

   Dramatic performance benefits were seen in some real world cases.

 - "JFS: Implement migrate_folio for jfs_metapage_aops" from Shivank
   Garg addresses a warning which occurs during memory compaction when
   using JFS.

 - "move all VMA allocation, freeing and duplication logic to mm" from
   Lorenzo Stoakes moves some VMA code from kernel/fork.c into the more
   appropriate mm/vma.c.

 - "mm, swap: clean up swap cache mapping helper" from Kairui Song
   provides code consolidation and cleanups related to the folio_index()
   function.

 - "mm/gup: Cleanup memfd_pin_folios()" from Vishal Moola does that.

 - "memcg: Fix test_memcg_min/low test failures" from Waiman Long
   addresses some bogus failures which are being reported by the
   test_memcontrol selftest.

 - "eliminate mmap() retry merge, add .mmap_prepare hook" from Lorenzo
   Stoakes commences the deprecation of file_operations.mmap() in favor
   of the new file_operations.mmap_prepare().

   The latter is more restrictive and prevents drivers from messing with
   things in ways which, amongst other problems, may defeat VMA merging.

 - "memcg: decouple memcg and objcg stocks"" from Shakeel Butt decouples
   the per-cpu memcg charge cache from the objcg's one.

   This is a step along the way to making memcg and objcg charging
   NMI-safe, which is a BPF requirement.

 - "mm/damon: minor fixups and improvements for code, tests, and
   documents" from SeongJae Park is yet another batch of miscellaneous
   DAMON changes. Fix and improve minor problems in code, tests and
   documents.

 - "memcg: make memcg stats irq safe" from Shakeel Butt converts memcg
   stats to be irq safe. Another step along the way to making memcg
   charging and stats updates NMI-safe, a BPF requirement.

 - "Let unmap_hugepage_range() and several related functions take folio
   instead of page" from Fan Ni provides folio conversions in the
   hugetlb code.

* tag 'mm-stable-2025-05-31-14-50' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (285 commits)
  mm: pcp: increase pcp->free_count threshold to trigger free_high
  mm/hugetlb: convert use of struct page to folio in __unmap_hugepage_range()
  mm/hugetlb: refactor __unmap_hugepage_range() to take folio instead of page
  mm/hugetlb: refactor unmap_hugepage_range() to take folio instead of page
  mm/hugetlb: pass folio instead of page to unmap_ref_private()
  memcg: objcg stock trylock without irq disabling
  memcg: no stock lock for cpu hot-unplug
  memcg: make __mod_memcg_lruvec_state re-entrant safe against irqs
  memcg: make count_memcg_events re-entrant safe against irqs
  memcg: make mod_memcg_state re-entrant safe against irqs
  memcg: move preempt disable to callers of memcg_rstat_updated
  memcg: memcg_rstat_updated re-entrant safe against irqs
  mm: khugepaged: decouple SHMEM and file folios' collapse
  selftests/eventfd: correct test name and improve messages
  alloc_tag: check mem_profiling_support in alloc_tag_init
  Docs/damon: update titles and brief introductions to explain DAMOS
  selftests/damon/_damon_sysfs: read tried regions directories in order
  mm/damon/tests/core-kunit: add a test for damos_set_filters_default_reject()
  mm/damon/paddr: remove unused variable, folio_list, in damon_pa_stat()
  mm/damon/sysfs-schemes: fix wrong comment on damons_sysfs_quota_goal_metric_strs
  ...

1 files changed, 1266 insertions, 0 deletions

diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
new file mode 100644
index 000000000000..69b953551677
--- /dev/null
+++ b/kernel/kexec_handover.c
@@ -0,0 +1,1266 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * kexec_handover.c - kexec handover metadata processing
+ * Copyright (C) 2023 Alexander Graf <graf@amazon.com>
+ * Copyright (C) 2025 Microsoft Corporation, Mike Rapoport <rppt@kernel.org>
+ * Copyright (C) 2025 Google LLC, Changyuan Lyu <changyuanl@google.com>
+ */
+
+#define pr_fmt(fmt) "KHO: " fmt
+
+#include <linux/cma.h>
+#include <linux/count_zeros.h>
+#include <linux/debugfs.h>
+#include <linux/kexec.h>
+#include <linux/kexec_handover.h>
+#include <linux/libfdt.h>
+#include <linux/list.h>
+#include <linux/memblock.h>
+#include <linux/notifier.h>
+#include <linux/page-isolation.h>
+
+#include <asm/early_ioremap.h>
+
+/*
+ * KHO is tightly coupled with mm init and needs access to some of mm
+ * internal APIs.
+ */
+#include "../mm/internal.h"
+#include "kexec_internal.h"
+
+#define KHO_FDT_COMPATIBLE "kho-v1"
+#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
+#define PROP_SUB_FDT "fdt"
+
+static bool kho_enable __ro_after_init;
+
+bool kho_is_enabled(void)
+{
+	return kho_enable;
+}
+EXPORT_SYMBOL_GPL(kho_is_enabled);
+
+static int __init kho_parse_enable(char *p)
+{
+	return kstrtobool(p, &kho_enable);
+}
+early_param("kho", kho_parse_enable);
+
+/*
+ * Keep track of memory that is to be preserved across KHO.
+ *
+ * The serializing side uses two levels of xarrays to manage chunks of per-order
+ * 512 byte bitmaps. For instance if PAGE_SIZE = 4096, the entire 1G order of a
+ * 1TB system would fit inside a single 512 byte bitmap. For order 0 allocations
+ * each bitmap will cover 16M of address space. Thus, for 16G of memory at most
+ * 512K of bitmap memory will be needed for order 0.
+ *
+ * This approach is fully incremental, as the serialization progresses folios
+ * can continue be aggregated to the tracker. The final step, immediately prior
+ * to kexec would serialize the xarray information into a linked list for the
+ * successor kernel to parse.
+ */
+
+#define PRESERVE_BITS (512 * 8)
+
+struct kho_mem_phys_bits {
+	DECLARE_BITMAP(preserve, PRESERVE_BITS);
+};
+
+struct kho_mem_phys {
+	/*
+	 * Points to kho_mem_phys_bits, a sparse bitmap array. Each bit is sized
+	 * to order.
+	 */
+	struct xarray phys_bits;
+};
+
+struct kho_mem_track {
+	/* Points to kho_mem_phys, each order gets its own bitmap tree */
+	struct xarray orders;
+};
+
+struct khoser_mem_chunk;
+
+struct kho_serialization {
+	struct page *fdt;
+	struct list_head fdt_list;
+	struct dentry *sub_fdt_dir;
+	struct kho_mem_track track;
+	/* First chunk of serialized preserved memory map */
+	struct khoser_mem_chunk *preserved_mem_map;
+};
+
+static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t sz)
+{
+	void *elm, *res;
+
+	elm = xa_load(xa, index);
+	if (elm)
+		return elm;
+
+	elm = kzalloc(sz, GFP_KERNEL);
+	if (!elm)
+		return ERR_PTR(-ENOMEM);
+
+	res = xa_cmpxchg(xa, index, NULL, elm, GFP_KERNEL);
+	if (xa_is_err(res))
+		res = ERR_PTR(xa_err(res));
+
+	if (res) {
+		kfree(elm);
+		return res;
+	}
+
+	return elm;
+}
+
+static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
+			     unsigned long end_pfn)
+{
+	struct kho_mem_phys_bits *bits;
+	struct kho_mem_phys *physxa;
+
+	while (pfn < end_pfn) {
+		const unsigned int order =
+			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
+		const unsigned long pfn_high = pfn >> order;
+
+		physxa = xa_load(&track->orders, order);
+		if (!physxa)
+			continue;
+
+		bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
+		if (!bits)
+			continue;
+
+		clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+
+		pfn += 1 << order;
+	}
+}
+
+static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
+				unsigned int order)
+{
+	struct kho_mem_phys_bits *bits;
+	struct kho_mem_phys *physxa;
+	const unsigned long pfn_high = pfn >> order;
+
+	might_sleep();
+
+	physxa = xa_load_or_alloc(&track->orders, order, sizeof(*physxa));
+	if (IS_ERR(physxa))
+		return PTR_ERR(physxa);
+
+	bits = xa_load_or_alloc(&physxa->phys_bits, pfn_high / PRESERVE_BITS,
+				sizeof(*bits));
+	if (IS_ERR(bits))
+		return PTR_ERR(bits);
+
+	set_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+
+	return 0;
+}
+
+/* almost as free_reserved_page(), just don't free the page */
+static void kho_restore_page(struct page *page)
+{
+	ClearPageReserved(page);
+	init_page_count(page);
+	adjust_managed_page_count(page, 1);
+}
+
+/**
+ * kho_restore_folio - recreates the folio from the preserved memory.
+ * @phys: physical address of the folio.
+ *
+ * Return: pointer to the struct folio on success, NULL on failure.
+ */
+struct folio *kho_restore_folio(phys_addr_t phys)
+{
+	struct page *page = pfn_to_online_page(PHYS_PFN(phys));
+	unsigned long order;
+
+	if (!page)
+		return NULL;
+
+	order = page->private;
+	if (order) {
+		if (order > MAX_PAGE_ORDER)
+			return NULL;
+
+		prep_compound_page(page, order);
+	} else {
+		kho_restore_page(page);
+	}
+
+	return page_folio(page);
+}
+EXPORT_SYMBOL_GPL(kho_restore_folio);
+
+/* Serialize and deserialize struct kho_mem_phys across kexec
+ *
+ * Record all the bitmaps in a linked list of pages for the next kernel to
+ * process. Each chunk holds bitmaps of the same order and each block of bitmaps
+ * starts at a given physical address. This allows the bitmaps to be sparse. The
+ * xarray is used to store them in a tree while building up the data structure,
+ * but the KHO successor kernel only needs to process them once in order.
+ *
+ * All of this memory is normal kmalloc() memory and is not marked for
+ * preservation. The successor kernel will remain isolated to the scratch space
+ * until it completes processing this list. Once processed all the memory
+ * storing these ranges will be marked as free.
+ */
+
+struct khoser_mem_bitmap_ptr {
+	phys_addr_t phys_start;
+	DECLARE_KHOSER_PTR(bitmap, struct kho_mem_phys_bits *);
+};
+
+struct khoser_mem_chunk_hdr {
+	DECLARE_KHOSER_PTR(next, struct khoser_mem_chunk *);
+	unsigned int order;
+	unsigned int num_elms;
+};
+
+#define KHOSER_BITMAP_SIZE                                   \
+	((PAGE_SIZE - sizeof(struct khoser_mem_chunk_hdr)) / \
+	 sizeof(struct khoser_mem_bitmap_ptr))
+
+struct khoser_mem_chunk {
+	struct khoser_mem_chunk_hdr hdr;
+	struct khoser_mem_bitmap_ptr bitmaps[KHOSER_BITMAP_SIZE];
+};
+
+static_assert(sizeof(struct khoser_mem_chunk) == PAGE_SIZE);
+
+static struct khoser_mem_chunk *new_chunk(struct khoser_mem_chunk *cur_chunk,
+					  unsigned long order)
+{
+	struct khoser_mem_chunk *chunk;
+
+	chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!chunk)
+		return NULL;
+	chunk->hdr.order = order;
+	if (cur_chunk)
+		KHOSER_STORE_PTR(cur_chunk->hdr.next, chunk);
+	return chunk;
+}
+
+static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk)
+{
+	struct khoser_mem_chunk *chunk = first_chunk;
+
+	while (chunk) {
+		struct khoser_mem_chunk *tmp = chunk;
+
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		kfree(tmp);
+	}
+}
+
+static int kho_mem_serialize(struct kho_serialization *ser)
+{
+	struct khoser_mem_chunk *first_chunk = NULL;
+	struct khoser_mem_chunk *chunk = NULL;
+	struct kho_mem_phys *physxa;
+	unsigned long order;
+
+	xa_for_each(&ser->track.orders, order, physxa) {
+		struct kho_mem_phys_bits *bits;
+		unsigned long phys;
+
+		chunk = new_chunk(chunk, order);
+		if (!chunk)
+			goto err_free;
+
+		if (!first_chunk)
+			first_chunk = chunk;
+
+		xa_for_each(&physxa->phys_bits, phys, bits) {
+			struct khoser_mem_bitmap_ptr *elm;
+
+			if (chunk->hdr.num_elms == ARRAY_SIZE(chunk->bitmaps)) {
+				chunk = new_chunk(chunk, order);
+				if (!chunk)
+					goto err_free;
+			}
+
+			elm = &chunk->bitmaps[chunk->hdr.num_elms];
+			chunk->hdr.num_elms++;
+			elm->phys_start = (phys * PRESERVE_BITS)
+					  << (order + PAGE_SHIFT);
+			KHOSER_STORE_PTR(elm->bitmap, bits);
+		}
+	}
+
+	ser->preserved_mem_map = first_chunk;
+
+	return 0;
+
+err_free:
+	kho_mem_ser_free(first_chunk);
+	return -ENOMEM;
+}
+
+static void deserialize_bitmap(unsigned int order,
+			       struct khoser_mem_bitmap_ptr *elm)
+{
+	struct kho_mem_phys_bits *bitmap = KHOSER_LOAD_PTR(elm->bitmap);
+	unsigned long bit;
+
+	for_each_set_bit(bit, bitmap->preserve, PRESERVE_BITS) {
+		int sz = 1 << (order + PAGE_SHIFT);
+		phys_addr_t phys =
+			elm->phys_start + (bit << (order + PAGE_SHIFT));
+		struct page *page = phys_to_page(phys);
+
+		memblock_reserve(phys, sz);
+		memblock_reserved_mark_noinit(phys, sz);
+		page->private = order;
+	}
+}
+
+static void __init kho_mem_deserialize(const void *fdt)
+{
+	struct khoser_mem_chunk *chunk;
+	const phys_addr_t *mem;
+	int len;
+
+	mem = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
+
+	if (!mem || len != sizeof(*mem)) {
+		pr_err("failed to get preserved memory bitmaps\n");
+		return;
+	}
+
+	chunk = *mem ? phys_to_virt(*mem) : NULL;
+	while (chunk) {
+		unsigned int i;
+
+		for (i = 0; i != chunk->hdr.num_elms; i++)
+			deserialize_bitmap(chunk->hdr.order,
+					   &chunk->bitmaps[i]);
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+	}
+}
+
+/*
+ * With KHO enabled, memory can become fragmented because KHO regions may
+ * be anywhere in physical address space. The scratch regions give us a
+ * safe zones that we will never see KHO allocations from. This is where we
+ * can later safely load our new kexec images into and then use the scratch
+ * area for early allocations that happen before page allocator is
+ * initialized.
+ */
+static struct kho_scratch *kho_scratch;
+static unsigned int kho_scratch_cnt;
+
+/*
+ * The scratch areas are scaled by default as percent of memory allocated from
+ * memblock. A user can override the scale with command line parameter:
+ *
+ * kho_scratch=N%
+ *
+ * It is also possible to explicitly define size for a lowmem, a global and
+ * per-node scratch areas:
+ *
+ * kho_scratch=l[KMG],n[KMG],m[KMG]
+ *
+ * The explicit size definition takes precedence over scale definition.
+ */
+static unsigned int scratch_scale __initdata = 200;
+static phys_addr_t scratch_size_global __initdata;
+static phys_addr_t scratch_size_pernode __initdata;
+static phys_addr_t scratch_size_lowmem __initdata;
+
+static int __init kho_parse_scratch_size(char *p)
+{
+	size_t len;
+	unsigned long sizes[3];
+	int i;
+
+	if (!p)
+		return -EINVAL;
+
+	len = strlen(p);
+	if (!len)
+		return -EINVAL;
+
+	/* parse nn% */
+	if (p[len - 1] == '%') {
+		/* unsigned int max is 4,294,967,295, 10 chars */
+		char s_scale[11] = {};
+		int ret = 0;
+
+		if (len > ARRAY_SIZE(s_scale))
+			return -EINVAL;
+
+		memcpy(s_scale, p, len - 1);
+		ret = kstrtouint(s_scale, 10, &scratch_scale);
+		if (!ret)
+			pr_notice("scratch scale is %d%%\n", scratch_scale);
+		return ret;
+	}
+
+	/* parse ll[KMG],mm[KMG],nn[KMG] */
+	for (i = 0; i < ARRAY_SIZE(sizes); i++) {
+		char *endp = p;
+
+		if (i > 0) {
+			if (*p != ',')
+				return -EINVAL;
+			p += 1;
+		}
+
+		sizes[i] = memparse(p, &endp);
+		if (!sizes[i] || endp == p)
+			return -EINVAL;
+		p = endp;
+	}
+
+	scratch_size_lowmem = sizes[0];
+	scratch_size_global = sizes[1];
+	scratch_size_pernode = sizes[2];
+	scratch_scale = 0;
+
+	pr_notice("scratch areas: lowmem: %lluMiB global: %lluMiB pernode: %lldMiB\n",
+		  (u64)(scratch_size_lowmem >> 20),
+		  (u64)(scratch_size_global >> 20),
+		  (u64)(scratch_size_pernode >> 20));
+
+	return 0;
+}
+early_param("kho_scratch", kho_parse_scratch_size);
+
+static void __init scratch_size_update(void)
+{
+	phys_addr_t size;
+
+	if (!scratch_scale)
+		return;
+
+	size = memblock_reserved_kern_size(ARCH_LOW_ADDRESS_LIMIT,
+					   NUMA_NO_NODE);
+	size = size * scratch_scale / 100;
+	scratch_size_lowmem = round_up(size, CMA_MIN_ALIGNMENT_BYTES);
+
+	size = memblock_reserved_kern_size(MEMBLOCK_ALLOC_ANYWHERE,
+					   NUMA_NO_NODE);
+	size = size * scratch_scale / 100 - scratch_size_lowmem;
+	scratch_size_global = round_up(size, CMA_MIN_ALIGNMENT_BYTES);
+}
+
+static phys_addr_t __init scratch_size_node(int nid)
+{
+	phys_addr_t size;
+
+	if (scratch_scale) {
+		size = memblock_reserved_kern_size(MEMBLOCK_ALLOC_ANYWHERE,
+						   nid);
+		size = size * scratch_scale / 100;
+	} else {
+		size = scratch_size_pernode;
+	}
+
+	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
+}
+
+/**
+ * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
+ *
+ * With KHO we can preserve arbitrary pages in the system. To ensure we still
+ * have a large contiguous region of memory when we search the physical address
+ * space for target memory, let's make sure we always have a large CMA region
+ * active. This CMA region will only be used for movable pages which are not a
+ * problem for us during KHO because we can just move them somewhere else.
+ */
+static void __init kho_reserve_scratch(void)
+{
+	phys_addr_t addr, size;
+	int nid, i = 0;
+
+	if (!kho_enable)
+		return;
+
+	scratch_size_update();
+
+	/* FIXME: deal with node hot-plug/remove */
+	kho_scratch_cnt = num_online_nodes() + 2;
+	size = kho_scratch_cnt * sizeof(*kho_scratch);
+	kho_scratch = memblock_alloc(size, PAGE_SIZE);
+	if (!kho_scratch)
+		goto err_disable_kho;
+
+	/*
+	 * reserve scratch area in low memory for lowmem allocations in the
+	 * next kernel
+	 */
+	size = scratch_size_lowmem;
+	addr = memblock_phys_alloc_range(size, CMA_MIN_ALIGNMENT_BYTES, 0,
+					 ARCH_LOW_ADDRESS_LIMIT);
+	if (!addr)
+		goto err_free_scratch_desc;
+
+	kho_scratch[i].addr = addr;
+	kho_scratch[i].size = size;
+	i++;
+
+	/* reserve large contiguous area for allocations without nid */
+	size = scratch_size_global;
+	addr = memblock_phys_alloc(size, CMA_MIN_ALIGNMENT_BYTES);
+	if (!addr)
+		goto err_free_scratch_areas;
+
+	kho_scratch[i].addr = addr;
+	kho_scratch[i].size = size;
+	i++;
+
+	for_each_online_node(nid) {
+		size = scratch_size_node(nid);
+		addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
+						0, MEMBLOCK_ALLOC_ACCESSIBLE,
+						nid, true);
+		if (!addr)
+			goto err_free_scratch_areas;
+
+		kho_scratch[i].addr = addr;
+		kho_scratch[i].size = size;
+		i++;
+	}
+
+	return;
+
+err_free_scratch_areas:
+	for (i--; i >= 0; i--)
+		memblock_phys_free(kho_scratch[i].addr, kho_scratch[i].size);
+err_free_scratch_desc:
+	memblock_free(kho_scratch, kho_scratch_cnt * sizeof(*kho_scratch));
+err_disable_kho:
+	kho_enable = false;
+}
+
+struct fdt_debugfs {
+	struct list_head list;
+	struct debugfs_blob_wrapper wrapper;
+	struct dentry *file;
+};
+
+static int kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
+			       const char *name, const void *fdt)
+{
+	struct fdt_debugfs *f;
+	struct dentry *file;
+
+	f = kmalloc(sizeof(*f), GFP_KERNEL);
+	if (!f)
+		return -ENOMEM;
+
+	f->wrapper.data = (void *)fdt;
+	f->wrapper.size = fdt_totalsize(fdt);
+
+	file = debugfs_create_blob(name, 0400, dir, &f->wrapper);
+	if (IS_ERR(file)) {
+		kfree(f);
+		return PTR_ERR(file);
+	}
+
+	f->file = file;
+	list_add(&f->list, list);
+
+	return 0;
+}
+
+/**
+ * kho_add_subtree - record the physical address of a sub FDT in KHO root tree.
+ * @ser: serialization control object passed by KHO notifiers.
+ * @name: name of the sub tree.
+ * @fdt: the sub tree blob.
+ *
+ * Creates a new child node named @name in KHO root FDT and records
+ * the physical address of @fdt. The pages of @fdt must also be preserved
+ * by KHO for the new kernel to retrieve it after kexec.
+ *
+ * A debugfs blob entry is also created at
+ * ``/sys/kernel/debug/kho/out/sub_fdts/@name``.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt)
+{
+	int err = 0;
+	u64 phys = (u64)virt_to_phys(fdt);
+	void *root = page_to_virt(ser->fdt);
+
+	err |= fdt_begin_node(root, name);
+	err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));
+	err |= fdt_end_node(root);
+
+	if (err)
+		return err;
+
+	return kho_debugfs_fdt_add(&ser->fdt_list, ser->sub_fdt_dir, name, fdt);
+}
+EXPORT_SYMBOL_GPL(kho_add_subtree);
+
+struct kho_out {
+	struct blocking_notifier_head chain_head;
+
+	struct dentry *dir;
+
+	struct mutex lock; /* protects KHO FDT finalization */
+
+	struct kho_serialization ser;
+	bool finalized;
+};
+
+static struct kho_out kho_out = {
+	.chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head),
+	.lock = __MUTEX_INITIALIZER(kho_out.lock),
+	.ser = {
+		.fdt_list = LIST_HEAD_INIT(kho_out.ser.fdt_list),
+		.track = {
+			.orders = XARRAY_INIT(kho_out.ser.track.orders, 0),
+		},
+	},
+	.finalized = false,
+};
+
+int register_kho_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&kho_out.chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(register_kho_notifier);
+
+int unregister_kho_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&kho_out.chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_kho_notifier);
+
+/**
+ * kho_preserve_folio - preserve a folio across kexec.
+ * @folio: folio to preserve.
+ *
+ * Instructs KHO to preserve the whole folio across kexec. The order
+ * will be preserved as well.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_preserve_folio(struct folio *folio)
+{
+	const unsigned long pfn = folio_pfn(folio);
+	const unsigned int order = folio_order(folio);
+	struct kho_mem_track *track = &kho_out.ser.track;
+
+	if (kho_out.finalized)
+		return -EBUSY;
+
+	return __kho_preserve_order(track, pfn, order);
+}
+EXPORT_SYMBOL_GPL(kho_preserve_folio);
+
+/**
+ * kho_preserve_phys - preserve a physically contiguous range across kexec.
+ * @phys: physical address of the range.
+ * @size: size of the range.
+ *
+ * Instructs KHO to preserve the memory range from @phys to @phys + @size
+ * across kexec.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_preserve_phys(phys_addr_t phys, size_t size)
+{
+	unsigned long pfn = PHYS_PFN(phys);
+	unsigned long failed_pfn = 0;
+	const unsigned long start_pfn = pfn;
+	const unsigned long end_pfn = PHYS_PFN(phys + size);
+	int err = 0;
+	struct kho_mem_track *track = &kho_out.ser.track;
+
+	if (kho_out.finalized)
+		return -EBUSY;
+
+	if (!PAGE_ALIGNED(phys) || !PAGE_ALIGNED(size))
+		return -EINVAL;
+
+	while (pfn < end_pfn) {
+		const unsigned int order =
+			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
+
+		err = __kho_preserve_order(track, pfn, order);
+		if (err) {
+			failed_pfn = pfn;
+			break;
+		}
+
+		pfn += 1 << order;
+	}
+
+	if (err)
+		__kho_unpreserve(track, start_pfn, failed_pfn);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(kho_preserve_phys);
+
+/* Handling for debug/kho/out */
+
+static struct dentry *debugfs_root;
+
+static int kho_out_update_debugfs_fdt(void)
+{
+	int err = 0;
+	struct fdt_debugfs *ff, *tmp;
+
+	if (kho_out.finalized) {
+		err = kho_debugfs_fdt_add(&kho_out.ser.fdt_list, kho_out.dir,
+					  "fdt", page_to_virt(kho_out.ser.fdt));
+	} else {
+		list_for_each_entry_safe(ff, tmp, &kho_out.ser.fdt_list, list) {
+			debugfs_remove(ff->file);
+			list_del(&ff->list);
+			kfree(ff);
+		}
+	}
+
+	return err;
+}
+
+static int kho_abort(void)
+{
+	int err;
+	unsigned long order;
+	struct kho_mem_phys *physxa;
+
+	xa_for_each(&kho_out.ser.track.orders, order, physxa) {
+		struct kho_mem_phys_bits *bits;
+		unsigned long phys;
+
+		xa_for_each(&physxa->phys_bits, phys, bits)
+			kfree(bits);
+
+		xa_destroy(&physxa->phys_bits);
+		kfree(physxa);
+	}
+	xa_destroy(&kho_out.ser.track.orders);
+
+	if (kho_out.ser.preserved_mem_map) {
+		kho_mem_ser_free(kho_out.ser.preserved_mem_map);
+		kho_out.ser.preserved_mem_map = NULL;
+	}
+
+	err = blocking_notifier_call_chain(&kho_out.chain_head, KEXEC_KHO_ABORT,
+					   NULL);
+	err = notifier_to_errno(err);
+
+	if (err)
+		pr_err("Failed to abort KHO finalization: %d\n", err);
+
+	return err;
+}
+
+static int kho_finalize(void)
+{
+	int err = 0;
+	u64 *preserved_mem_map;
+	void *fdt = page_to_virt(kho_out.ser.fdt);
+
+	err |= fdt_create(fdt, PAGE_SIZE);
+	err |= fdt_finish_reservemap(fdt);
+	err |= fdt_begin_node(fdt, "");
+	err |= fdt_property_string(fdt, "compatible", KHO_FDT_COMPATIBLE);
+	/**
+	 * Reserve the preserved-memory-map property in the root FDT, so
+	 * that all property definitions will precede subnodes created by
+	 * KHO callers.
+	 */
+	err |= fdt_property_placeholder(fdt, PROP_PRESERVED_MEMORY_MAP,
+					sizeof(*preserved_mem_map),
+					(void **)&preserved_mem_map);
+	if (err)
+		goto abort;
+
+	err = kho_preserve_folio(page_folio(kho_out.ser.fdt));
+	if (err)
+		goto abort;
+
+	err = blocking_notifier_call_chain(&kho_out.chain_head,
+					   KEXEC_KHO_FINALIZE, &kho_out.ser);
+	err = notifier_to_errno(err);
+	if (err)
+		goto abort;
+
+	err = kho_mem_serialize(&kho_out.ser);
+	if (err)
+		goto abort;
+
+	*preserved_mem_map = (u64)virt_to_phys(kho_out.ser.preserved_mem_map);
+
+	err |= fdt_end_node(fdt);
+	err |= fdt_finish(fdt);
+
+abort:
+	if (err) {
+		pr_err("Failed to convert KHO state tree: %d\n", err);
+		kho_abort();
+	}
+
+	return err;
+}
+
+static int kho_out_finalize_get(void *data, u64 *val)
+{
+	mutex_lock(&kho_out.lock);
+	*val = kho_out.finalized;
+	mutex_unlock(&kho_out.lock);
+
+	return 0;
+}
+
+static int kho_out_finalize_set(void *data, u64 _val)
+{
+	int ret = 0;
+	bool val = !!_val;
+
+	mutex_lock(&kho_out.lock);
+
+	if (val == kho_out.finalized) {
+		if (kho_out.finalized)
+			ret = -EEXIST;
+		else
+			ret = -ENOENT;
+		goto unlock;
+	}
+
+	if (val)
+		ret = kho_finalize();
+	else
+		ret = kho_abort();
+
+	if (ret)
+		goto unlock;
+
+	kho_out.finalized = val;
+	ret = kho_out_update_debugfs_fdt();
+
+unlock:
+	mutex_unlock(&kho_out.lock);
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
+			 kho_out_finalize_set, "%llu\n");
+
+static int scratch_phys_show(struct seq_file *m, void *v)
+{
+	for (int i = 0; i < kho_scratch_cnt; i++)
+		seq_printf(m, "0x%llx\n", kho_scratch[i].addr);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(scratch_phys);
+
+static int scratch_len_show(struct seq_file *m, void *v)
+{
+	for (int i = 0; i < kho_scratch_cnt; i++)
+		seq_printf(m, "0x%llx\n", kho_scratch[i].size);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(scratch_len);
+
+static __init int kho_out_debugfs_init(void)
+{
+	struct dentry *dir, *f, *sub_fdt_dir;
+
+	dir = debugfs_create_dir("out", debugfs_root);
+	if (IS_ERR(dir))
+		return -ENOMEM;
+
+	sub_fdt_dir = debugfs_create_dir("sub_fdts", dir);
+	if (IS_ERR(sub_fdt_dir))
+		goto err_rmdir;
+
+	f = debugfs_create_file("scratch_phys", 0400, dir, NULL,
+				&scratch_phys_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	f = debugfs_create_file("scratch_len", 0400, dir, NULL,
+				&scratch_len_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	f = debugfs_create_file("finalize", 0600, dir, NULL,
+				&fops_kho_out_finalize);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
+	kho_out.dir = dir;
+	kho_out.ser.sub_fdt_dir = sub_fdt_dir;
+	return 0;
+
+err_rmdir:
+	debugfs_remove_recursive(dir);
+	return -ENOENT;
+}
+
+struct kho_in {
+	struct dentry *dir;
+	phys_addr_t fdt_phys;
+	phys_addr_t scratch_phys;
+	struct list_head fdt_list;
+};
+
+static struct kho_in kho_in = {
+	.fdt_list = LIST_HEAD_INIT(kho_in.fdt_list),
+};
+
+static const void *kho_get_fdt(void)
+{
+	return kho_in.fdt_phys ? phys_to_virt(kho_in.fdt_phys) : NULL;
+}
+
+/**
+ * kho_retrieve_subtree - retrieve a preserved sub FDT by its name.
+ * @name: the name of the sub FDT passed to kho_add_subtree().
+ * @phys: if found, the physical address of the sub FDT is stored in @phys.
+ *
+ * Retrieve a preserved sub FDT named @name and store its physical
+ * address in @phys.
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_retrieve_subtree(const char *name, phys_addr_t *phys)
+{
+	const void *fdt = kho_get_fdt();
+	const u64 *val;
+	int offset, len;
+
+	if (!fdt)
+		return -ENOENT;
+
+	if (!phys)
+		return -EINVAL;
+
+	offset = fdt_subnode_offset(fdt, 0, name);
+	if (offset < 0)
+		return -ENOENT;
+
+	val = fdt_getprop(fdt, offset, PROP_SUB_FDT, &len);
+	if (!val || len != sizeof(*val))
+		return -EINVAL;
+
+	*phys = (phys_addr_t)*val;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
+
+/* Handling for debugfs/kho/in */
+
+static __init int kho_in_debugfs_init(const void *fdt)
+{
+	struct dentry *sub_fdt_dir;
+	int err, child;
+
+	kho_in.dir = debugfs_create_dir("in", debugfs_root);
+	if (IS_ERR(kho_in.dir))
+		return PTR_ERR(kho_in.dir);
+
+	sub_fdt_dir = debugfs_create_dir("sub_fdts", kho_in.dir);
+	if (IS_ERR(sub_fdt_dir)) {
+		err = PTR_ERR(sub_fdt_dir);
+		goto err_rmdir;
+	}
+
+	err = kho_debugfs_fdt_add(&kho_in.fdt_list, kho_in.dir, "fdt", fdt);
+	if (err)
+		goto err_rmdir;
+
+	fdt_for_each_subnode(child, fdt, 0) {
+		int len = 0;
+		const char *name = fdt_get_name(fdt, child, NULL);
+		const u64 *fdt_phys;
+
+		fdt_phys = fdt_getprop(fdt, child, "fdt", &len);
+		if (!fdt_phys)
+			continue;
+		if (len != sizeof(*fdt_phys)) {
+			pr_warn("node `%s`'s prop `fdt` has invalid length: %d\n",
+				name, len);
+			continue;
+		}
+		err = kho_debugfs_fdt_add(&kho_in.fdt_list, sub_fdt_dir, name,
+					  phys_to_virt(*fdt_phys));
+		if (err) {
+			pr_warn("failed to add fdt `%s` to debugfs: %d\n", name,
+				err);
+			continue;
+		}
+	}
+
+	return 0;
+
+err_rmdir:
+	debugfs_remove_recursive(kho_in.dir);
+	return err;
+}
+
+static __init int kho_init(void)
+{
+	int err = 0;
+	const void *fdt = kho_get_fdt();
+
+	if (!kho_enable)
+		return 0;
+
+	kho_out.ser.fdt = alloc_page(GFP_KERNEL);
+	if (!kho_out.ser.fdt) {
+		err = -ENOMEM;
+		goto err_free_scratch;
+	}
+
+	debugfs_root = debugfs_create_dir("kho", NULL);
+	if (IS_ERR(debugfs_root)) {
+		err = -ENOENT;
+		goto err_free_fdt;
+	}
+
+	err = kho_out_debugfs_init();
+	if (err)
+		goto err_free_fdt;
+
+	if (fdt) {
+		err = kho_in_debugfs_init(fdt);
+		/*
+		 * Failure to create /sys/kernel/debug/kho/in does not prevent
+		 * reviving state from KHO and setting up KHO for the next
+		 * kexec.
+		 */
+		if (err)
+			pr_err("failed exposing handover FDT in debugfs: %d\n",
+			       err);
+
+		return 0;
+	}
+
+	for (int i = 0; i < kho_scratch_cnt; i++) {
+		unsigned long base_pfn = PHYS_PFN(kho_scratch[i].addr);
+		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
+		unsigned long pfn;
+
+		for (pfn = base_pfn; pfn < base_pfn + count;
+		     pfn += pageblock_nr_pages)
+			init_cma_reserved_pageblock(pfn_to_page(pfn));
+	}
+
+	return 0;
+
+err_free_fdt:
+	put_page(kho_out.ser.fdt);
+	kho_out.ser.fdt = NULL;
+err_free_scratch:
+	for (int i = 0; i < kho_scratch_cnt; i++) {
+		void *start = __va(kho_scratch[i].addr);
+		void *end = start + kho_scratch[i].size;
+
+		free_reserved_area(start, end, -1, "");
+	}
+	kho_enable = false;
+	return err;
+}
+late_initcall(kho_init);
+
+static void __init kho_release_scratch(void)
+{
+	phys_addr_t start, end;
+	u64 i;
+
+	memmap_init_kho_scratch_pages();
+
+	/*
+	 * Mark scratch mem as CMA before we return it. That way we
+	 * ensure that no kernel allocations happen on it. That means
+	 * we can reuse it as scratch memory again later.
+	 */
+	__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
+			     MEMBLOCK_KHO_SCRATCH, &start, &end, NULL) {
+		ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
+		ulong end_pfn = pageblock_align(PFN_UP(end));
+		ulong pfn;
+
+		for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages)
+			set_pageblock_migratetype(pfn_to_page(pfn),
+						  MIGRATE_CMA);
+	}
+}
+
+void __init kho_memory_init(void)
+{
+	struct folio *folio;
+
+	if (kho_in.scratch_phys) {
+		kho_scratch = phys_to_virt(kho_in.scratch_phys);
+		kho_release_scratch();
+
+		kho_mem_deserialize(kho_get_fdt());
+		folio = kho_restore_folio(kho_in.fdt_phys);
+		if (!folio)
+			pr_warn("failed to restore folio for KHO fdt\n");
+	} else {
+		kho_reserve_scratch();
+	}
+}
+
+void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
+			 phys_addr_t scratch_phys, u64 scratch_len)
+{
+	void *fdt = NULL;
+	struct kho_scratch *scratch = NULL;
+	int err = 0;
+	unsigned int scratch_cnt = scratch_len / sizeof(*kho_scratch);
+
+	/* Validate the input FDT */
+	fdt = early_memremap(fdt_phys, fdt_len);
+	if (!fdt) {
+		pr_warn("setup: failed to memremap FDT (0x%llx)\n", fdt_phys);
+		err = -EFAULT;
+		goto out;
+	}
+	err = fdt_check_header(fdt);
+	if (err) {
+		pr_warn("setup: handover FDT (0x%llx) is invalid: %d\n",
+			fdt_phys, err);
+		err = -EINVAL;
+		goto out;
+	}
+	err = fdt_node_check_compatible(fdt, 0, KHO_FDT_COMPATIBLE);
+	if (err) {
+		pr_warn("setup: handover FDT (0x%llx) is incompatible with '%s': %d\n",
+			fdt_phys, KHO_FDT_COMPATIBLE, err);
+		err = -EINVAL;
+		goto out;
+	}
+
+	scratch = early_memremap(scratch_phys, scratch_len);
+	if (!scratch) {
+		pr_warn("setup: failed to memremap scratch (phys=0x%llx, len=%lld)\n",
+			scratch_phys, scratch_len);
+		err = -EFAULT;
+		goto out;
+	}
+
+	/*
+	 * We pass a safe contiguous blocks of memory to use for early boot
+	 * purporses from the previous kernel so that we can resize the
+	 * memblock array as needed.
+	 */
+	for (int i = 0; i < scratch_cnt; i++) {
+		struct kho_scratch *area = &scratch[i];
+		u64 size = area->size;
+
+		memblock_add(area->addr, size);
+		err = memblock_mark_kho_scratch(area->addr, size);
+		if (WARN_ON(err)) {
+			pr_warn("failed to mark the scratch region 0x%pa+0x%pa: %d",
+				&area->addr, &size, err);
+			goto out;
+		}
+		pr_debug("Marked 0x%pa+0x%pa as scratch", &area->addr, &size);
+	}
+
+	memblock_reserve(scratch_phys, scratch_len);
+
+	/*
+	 * Now that we have a viable region of scratch memory, let's tell
+	 * the memblocks allocator to only use that for any allocations.
+	 * That way we ensure that nothing scribbles over in use data while
+	 * we initialize the page tables which we will need to ingest all
+	 * memory reservations from the previous kernel.
+	 */
+	memblock_set_kho_scratch_only();
+
+	kho_in.fdt_phys = fdt_phys;
+	kho_in.scratch_phys = scratch_phys;
+	kho_scratch_cnt = scratch_cnt;
+	pr_info("found kexec handover data. Will skip init for some devices\n");
+
+out:
+	if (fdt)
+		early_memunmap(fdt, fdt_len);
+	if (scratch)
+		early_memunmap(scratch, scratch_len);
+	if (err)
+		pr_warn("disabling KHO revival: %d\n", err);
+}
+
+/* Helper functions for kexec_file_load */
+
+int kho_fill_kimage(struct kimage *image)
+{
+	ssize_t scratch_size;
+	int err = 0;
+	struct kexec_buf scratch;
+
+	if (!kho_enable)
+		return 0;
+
+	image->kho.fdt = page_to_phys(kho_out.ser.fdt);
+
+	scratch_size = sizeof(*kho_scratch) * kho_scratch_cnt;
+	scratch = (struct kexec_buf){
+		.image = image,
+		.buffer = kho_scratch,
+		.bufsz = scratch_size,
+		.mem = KEXEC_BUF_MEM_UNKNOWN,
+		.memsz = scratch_size,
+		.buf_align = SZ_64K, /* Makes it easier to map */
+		.buf_max = ULONG_MAX,
+		.top_down = true,
+	};
+	err = kexec_add_buffer(&scratch);
+	if (err)
+		return err;
+	image->kho.scratch = &image->segment[image->nr_segments - 1];
+
+	return 0;
+}
+
+static int kho_walk_scratch(struct kexec_buf *kbuf,
+			    int (*func)(struct resource *, void *))
+{
+	int ret = 0;
+	int i;
+
+	for (i = 0; i < kho_scratch_cnt; i++) {
+		struct resource res = {
+			.start = kho_scratch[i].addr,
+			.end = kho_scratch[i].addr + kho_scratch[i].size - 1,
+		};
+
+		/* Try to fit the kimage into our KHO scratch region */
+		ret = func(&res, kbuf);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
+int kho_locate_mem_hole(struct kexec_buf *kbuf,
+			int (*func)(struct resource *, void *))
+{
+	int ret;
+
+	if (!kho_enable || kbuf->image->type == KEXEC_TYPE_CRASH)
+		return 1;
+
+	ret = kho_walk_scratch(kbuf, func);
+
+	return ret == 1 ? 0 : -EADDRNOTAVAIL;
+}