kho: add support for preserving vmalloc allocations

A vmalloc allocation is preserved using binary structure similar to global
KHO memory tracker.  It's a linked list of pages where each page is an
array of physical address of pages in vmalloc area.

kho_preserve_vmalloc() hands out the physical address of the head page to
the caller.  This address is used as the argument to kho_vmalloc_restore()
to restore the mapping in the vmalloc address space and populate it with
the preserved pages.

[pasha.tatashin@soleen.com: free chunks using free_page() not kfree()]
  Link: https://lkml.kernel.org/r/mafs0a52idbeg.fsf@kernel.org
[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20250921054458.4043761-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: rppt

include/linux/kexec_handover.h

@@ -39,13 +39,24 @@ struct page;
 
 struct kho_serialization;
 
+struct kho_vmalloc_chunk;
+struct kho_vmalloc {
+	DECLARE_KHOSER_PTR(first, struct kho_vmalloc_chunk *);
+	unsigned int total_pages;
+	unsigned short flags;
+	unsigned short order;
+};
+
 #ifdef CONFIG_KEXEC_HANDOVER
 bool kho_is_enabled(void);
 bool is_kho_boot(void);
 
 int kho_preserve_folio(struct folio *folio);
 int kho_preserve_pages(struct page *page, unsigned int nr_pages);
+int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);
 struct folio *kho_restore_folio(phys_addr_t phys);
+struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages);
+void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
 int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt);
 int kho_retrieve_subtree(const char *name, phys_addr_t *phys);
 
@@ -77,11 +88,28 @@ static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_preserve_vmalloc(void *ptr,
+				       struct kho_vmalloc *preservation)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline struct folio *kho_restore_folio(phys_addr_t phys)
 {
 	return NULL;
 }
 
+static inline struct page *kho_restore_pages(phys_addr_t phys,
+					     unsigned int nr_pages)
+{
+	return NULL;
+}
+
+static inline void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)
+{
+	return NULL;
+}
+
 static inline int kho_add_subtree(struct kho_serialization *ser,
 				  const char *name, void *fdt)
 {

kernel/kexec_handover.c

@@ -18,6 +18,7 @@
 #include <linux/memblock.h>
 #include <linux/notifier.h>
 #include <linux/page-isolation.h>
+#include <linux/vmalloc.h>
 
 #include <asm/early_ioremap.h>
 
@@ -274,6 +275,37 @@ struct folio *kho_restore_folio(phys_addr_t phys)
 }
 EXPORT_SYMBOL_GPL(kho_restore_folio);
 
+/**
+ * kho_restore_pages - restore list of contiguous order 0 pages.
+ * @phys: physical address of the first page.
+ * @nr_pages: number of pages.
+ *
+ * Restore a contiguous list of order 0 pages that was preserved with
+ * kho_preserve_pages().
+ *
+ * Return: 0 on success, error code on failure
+ */
+struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages)
+{
+	const unsigned long start_pfn = PHYS_PFN(phys);
+	const unsigned long end_pfn = start_pfn + nr_pages;
+	unsigned long pfn = start_pfn;
+
+	while (pfn < end_pfn) {
+		const unsigned int order =
+			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
+		struct page *page = kho_restore_page(PFN_PHYS(pfn));
+
+		if (!page)
+			return NULL;
+		split_page(page, order);
+		pfn += 1 << order;
+	}
+
+	return pfn_to_page(start_pfn);
+}
+EXPORT_SYMBOL_GPL(kho_restore_pages);
+
 /* Serialize and deserialize struct kho_mem_phys across kexec
  *
  * Record all the bitmaps in a linked list of pages for the next kernel to
@@ -763,6 +795,255 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages)
 }
 EXPORT_SYMBOL_GPL(kho_preserve_pages);
 
+struct kho_vmalloc_hdr {
+	DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
+};
+
+#define KHO_VMALLOC_SIZE				\
+	((PAGE_SIZE - sizeof(struct kho_vmalloc_hdr)) / \
+	 sizeof(phys_addr_t))
+
+struct kho_vmalloc_chunk {
+	struct kho_vmalloc_hdr hdr;
+	phys_addr_t phys[KHO_VMALLOC_SIZE];
+};
+
+static_assert(sizeof(struct kho_vmalloc_chunk) == PAGE_SIZE);
+
+/* vmalloc flags KHO supports */
+#define KHO_VMALLOC_SUPPORTED_FLAGS	(VM_ALLOC | VM_ALLOW_HUGE_VMAP)
+
+/* KHO internal flags for vmalloc preservations */
+#define KHO_VMALLOC_ALLOC	0x0001
+#define KHO_VMALLOC_HUGE_VMAP	0x0002
+
+static unsigned short vmalloc_flags_to_kho(unsigned int vm_flags)
+{
+	unsigned short kho_flags = 0;
+
+	if (vm_flags & VM_ALLOC)
+		kho_flags |= KHO_VMALLOC_ALLOC;
+	if (vm_flags & VM_ALLOW_HUGE_VMAP)
+		kho_flags |= KHO_VMALLOC_HUGE_VMAP;
+
+	return kho_flags;
+}
+
+static unsigned int kho_flags_to_vmalloc(unsigned short kho_flags)
+{
+	unsigned int vm_flags = 0;
+
+	if (kho_flags & KHO_VMALLOC_ALLOC)
+		vm_flags |= VM_ALLOC;
+	if (kho_flags & KHO_VMALLOC_HUGE_VMAP)
+		vm_flags |= VM_ALLOW_HUGE_VMAP;
+
+	return vm_flags;
+}
+
+static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)
+{
+	struct kho_vmalloc_chunk *chunk;
+	int err;
+
+	chunk = (struct kho_vmalloc_chunk *)get_zeroed_page(GFP_KERNEL);
+	if (!chunk)
+		return NULL;
+
+	err = kho_preserve_pages(virt_to_page(chunk), 1);
+	if (err)
+		goto err_free;
+	if (cur)
+		KHOSER_STORE_PTR(cur->hdr.next, chunk);
+	return chunk;
+
+err_free:
+	free_page((unsigned long)chunk);
+	return NULL;
+}
+
+static void kho_vmalloc_unpreserve_chunk(struct kho_vmalloc_chunk *chunk)
+{
+	struct kho_mem_track *track = &kho_out.ser.track;
+	unsigned long pfn = PHYS_PFN(virt_to_phys(chunk));
+
+	__kho_unpreserve(track, pfn, pfn + 1);
+
+	for (int i = 0; chunk->phys[i]; i++) {
+		pfn = PHYS_PFN(chunk->phys[i]);
+		__kho_unpreserve(track, pfn, pfn + 1);
+	}
+}
+
+static void kho_vmalloc_free_chunks(struct kho_vmalloc *kho_vmalloc)
+{
+	struct kho_vmalloc_chunk *chunk = KHOSER_LOAD_PTR(kho_vmalloc->first);
+
+	while (chunk) {
+		struct kho_vmalloc_chunk *tmp = chunk;
+
+		kho_vmalloc_unpreserve_chunk(chunk);
+
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		free_page((unsigned long)tmp);
+	}
+}
+
+/**
+ * kho_preserve_vmalloc - preserve memory allocated with vmalloc() across kexec
+ * @ptr: pointer to the area in vmalloc address space
+ * @preservation: placeholder for preservation metadata
+ *
+ * Instructs KHO to preserve the area in vmalloc address space at @ptr. The
+ * physical pages mapped at @ptr will be preserved and on successful return
+ * @preservation will hold the physical address of a structure that describes
+ * the preservation.
+ *
+ * NOTE: The memory allocated with vmalloc_node() variants cannot be reliably
+ * restored on the same node
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation)
+{
+	struct kho_vmalloc_chunk *chunk;
+	struct vm_struct *vm = find_vm_area(ptr);
+	unsigned int order, flags, nr_contig_pages;
+	unsigned int idx = 0;
+	int err;
+
+	if (!vm)
+		return -EINVAL;
+
+	if (vm->flags & ~KHO_VMALLOC_SUPPORTED_FLAGS)
+		return -EOPNOTSUPP;
+
+	flags = vmalloc_flags_to_kho(vm->flags);
+	order = get_vm_area_page_order(vm);
+
+	chunk = new_vmalloc_chunk(NULL);
+	if (!chunk)
+		return -ENOMEM;
+	KHOSER_STORE_PTR(preservation->first, chunk);
+
+	nr_contig_pages = (1 << order);
+	for (int i = 0; i < vm->nr_pages; i += nr_contig_pages) {
+		phys_addr_t phys = page_to_phys(vm->pages[i]);
+
+		err = kho_preserve_pages(vm->pages[i], nr_contig_pages);
+		if (err)
+			goto err_free;
+
+		chunk->phys[idx++] = phys;
+		if (idx == ARRAY_SIZE(chunk->phys)) {
+			chunk = new_vmalloc_chunk(chunk);
+			if (!chunk)
+				goto err_free;
+			idx = 0;
+		}
+	}
+
+	preservation->total_pages = vm->nr_pages;
+	preservation->flags = flags;
+	preservation->order = order;
+
+	return 0;
+
+err_free:
+	kho_vmalloc_free_chunks(preservation);
+	return err;
+}
+EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
+
+/**
+ * kho_restore_vmalloc - recreates and populates an area in vmalloc address
+ * space from the preserved memory.
+ * @preservation: preservation metadata.
+ *
+ * Recreates an area in vmalloc address space and populates it with memory that
+ * was preserved using kho_preserve_vmalloc().
+ *
+ * Return: pointer to the area in the vmalloc address space, NULL on failure.
+ */
+void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)
+{
+	struct kho_vmalloc_chunk *chunk = KHOSER_LOAD_PTR(preservation->first);
+	unsigned int align, order, shift, vm_flags;
+	unsigned long total_pages, contig_pages;
+	unsigned long addr, size;
+	struct vm_struct *area;
+	struct page **pages;
+	unsigned int idx = 0;
+	int err;
+
+	vm_flags = kho_flags_to_vmalloc(preservation->flags);
+	if (vm_flags & ~KHO_VMALLOC_SUPPORTED_FLAGS)
+		return NULL;
+
+	total_pages = preservation->total_pages;
+	pages = kvmalloc_array(total_pages, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		return NULL;
+	order = preservation->order;
+	contig_pages = (1 << order);
+	shift = PAGE_SHIFT + order;
+	align = 1 << shift;
+
+	while (chunk) {
+		struct page *page;
+
+		for (int i = 0; chunk->phys[i]; i++) {
+			phys_addr_t phys = chunk->phys[i];
+
+			if (idx + contig_pages > total_pages)
+				goto err_free_pages_array;
+
+			page = kho_restore_pages(phys, contig_pages);
+			if (!page)
+				goto err_free_pages_array;
+
+			for (int j = 0; j < contig_pages; j++)
+				pages[idx++] = page;
+
+			phys += contig_pages * PAGE_SIZE;
+		}
+
+		page = kho_restore_pages(virt_to_phys(chunk), 1);
+		if (!page)
+			goto err_free_pages_array;
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		__free_page(page);
+	}
+
+	if (idx != total_pages)
+		goto err_free_pages_array;
+
+	area = __get_vm_area_node(total_pages * PAGE_SIZE, align, shift,
+				  vm_flags, VMALLOC_START, VMALLOC_END,
+				  NUMA_NO_NODE, GFP_KERNEL,
+				  __builtin_return_address(0));
+	if (!area)
+		goto err_free_pages_array;
+
+	addr = (unsigned long)area->addr;
+	size = get_vm_area_size(area);
+	err = vmap_pages_range(addr, addr + size, PAGE_KERNEL, pages, shift);
+	if (err)
+		goto err_free_vm_area;
+
+	area->nr_pages = total_pages;
+	area->pages = pages;
+
+	return area->addr;
+
+err_free_vm_area:
+	free_vm_area(area);
+err_free_pages_array:
+	kvfree(pages);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
+
 /* Handling for debug/kho/out */
 
 static struct dentry *debugfs_root;