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Message-ID: <20251209025317.3846938-3-jasonmiu@google.com>
Date: Mon, 8 Dec 2025 18:53:14 -0800
From: Jason Miu <jasonmiu@...gle.com>
To: Alexander Graf <graf@...zon.com>, Andrew Morton <akpm@...ux-foundation.org>,
Baoquan He <bhe@...hat.com>, Changyuan Lyu <changyuanl@...gle.com>,
David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>,
Jason Gunthorpe <jgg@...dia.com>, Jason Miu <jasonmiu@...gle.com>, Mike Rapoport <rppt@...nel.org>,
Pasha Tatashin <pasha.tatashin@...een.com>, Pratyush Yadav <pratyush@...nel.org>,
kexec@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v3 2/4] kho: Relocate vmalloc preservation structure to KHO
ABI header
The `struct kho_vmalloc` defines the in-memory layout for preserving
vmalloc regions across kexec. This layout is a contract between kernels
and part of the KHO ABI.
To reflect this relationship, the related structs and helper macros are
relocated to the ABI header, `include/linux/kho/abi/kexec_handover.h`.
This move places the structure's definition under the protection of the
KHO_FDT_COMPATIBLE version string.
The structure and its components are now also documented within the
ABI header to describe the contract and prevent ABI breaks.
Signed-off-by: Jason Miu <jasonmiu@...gle.com>
---
Documentation/core-api/kho/fdt.rst | 6 ++
include/linux/kexec_handover.h | 27 +--------
include/linux/kho/abi/kexec_handover.h | 78 ++++++++++++++++++++++++++
include/linux/kho/abi/memfd.h | 2 +-
kernel/liveupdate/kexec_handover.c | 15 -----
lib/test_kho.c | 1 +
6 files changed, 88 insertions(+), 41 deletions(-)
diff --git a/Documentation/core-api/kho/fdt.rst b/Documentation/core-api/kho/fdt.rst
index 4e080ccc420e..4202b67fcdf9 100644
--- a/Documentation/core-api/kho/fdt.rst
+++ b/Documentation/core-api/kho/fdt.rst
@@ -14,6 +14,12 @@ directly in the ABI header file.
.. kernel-doc:: include/linux/kho/abi/kexec_handover.h
:doc: Kexec Handover ABI
+Kexec Handover ABI for vmalloc Preservation
+===========================================
+
+.. kernel-doc:: include/linux/kho/abi/kexec_handover.h
+ :doc: Kexec Handover ABI for vmalloc Preservation
+
See Also
========
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 5f7b9de97e8d..a56ff3ffaf17 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -11,34 +11,11 @@ struct kho_scratch {
phys_addr_t size;
};
+struct kho_vmalloc;
+
struct folio;
struct page;
-#define DECLARE_KHOSER_PTR(name, type) \
- union { \
- phys_addr_t phys; \
- type ptr; \
- } name
-#define KHOSER_STORE_PTR(dest, val) \
- ({ \
- typeof(val) v = val; \
- typecheck(typeof((dest).ptr), v); \
- (dest).phys = virt_to_phys(v); \
- })
-#define KHOSER_LOAD_PTR(src) \
- ({ \
- typeof(src) s = src; \
- (typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \
- })
-
-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);
diff --git a/include/linux/kho/abi/kexec_handover.h b/include/linux/kho/abi/kexec_handover.h
index d78df2d44cb6..74f4fa67e458 100644
--- a/include/linux/kho/abi/kexec_handover.h
+++ b/include/linux/kho/abi/kexec_handover.h
@@ -10,6 +10,8 @@
#ifndef _LINUX_KHO_ABI_KEXEC_HANDOVER_H
#define _LINUX_KHO_ABI_KEXEC_HANDOVER_H
+#include <linux/types.h>
+
/**
* DOC: Kexec Handover ABI
*
@@ -81,4 +83,80 @@
/* The FDT property for sub-FDTs. */
#define KHO_FDT_SUB_TREE_PROP_NAME "fdt"
+/**
+ * DOC: Kexec Handover ABI for vmalloc Preservation
+ *
+ * The Kexec Handover ABI for preserving vmalloc'ed memory is defined by
+ * a set of structures and helper macros. The layout of these structures is a
+ * stable contract between kernels and is versioned by the KHO_FDT_COMPATIBLE
+ * string.
+ *
+ * The preservation is managed through a main descriptor struct (`kho_vmalloc`),
+ * which points to a linked list of `kho_vmalloc_chunk` structures. These
+ * chunks contain the physical addresses of the preserved pages, allowing the
+ * next kernel to reconstruct the vmalloc area with the same content and layout.
+ * Helper macros are also defined for storing and loading pointers within
+ * these structures.
+ */
+
+/* Helper macro to define a union for a serializable pointer. */
+#define DECLARE_KHOSER_PTR(name, type) \
+ union { \
+ u64 phys; \
+ type ptr; \
+ } name
+
+/* Stores the physical address of a serializable pointer. */
+#define KHOSER_STORE_PTR(dest, val) \
+ ({ \
+ typeof(val) v = val; \
+ typecheck(typeof((dest).ptr), v); \
+ (dest).phys = virt_to_phys(v); \
+ })
+
+/* Loads the stored physical address back to a pointer. */
+#define KHOSER_LOAD_PTR(src) \
+ ({ \
+ typeof(src) s = src; \
+ (typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \
+ })
+
+/*
+ * This header is embedded at the beginning of each `kho_vmalloc_chunk`
+ * and contains a pointer to the next chunk in the linked list,
+ * stored as a physical address for handover.
+ */
+struct kho_vmalloc_hdr {
+ DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
+};
+
+#define KHO_VMALLOC_SIZE \
+ ((PAGE_SIZE - sizeof(struct kho_vmalloc_hdr)) / \
+ sizeof(u64))
+
+/*
+ * Each chunk is a single page and is part of a linked list that describes
+ * a preserved vmalloc area. It contains the header with the link to the next
+ * chunk and an array of physical addresses of the pages that make up the
+ * preserved vmalloc area.
+ */
+struct kho_vmalloc_chunk {
+ struct kho_vmalloc_hdr hdr;
+ u64 phys[KHO_VMALLOC_SIZE];
+};
+
+static_assert(sizeof(struct kho_vmalloc_chunk) == PAGE_SIZE);
+
+/*
+ * Describes a preserved vmalloc memory area, including the
+ * total number of pages, allocation flags, page order, and a pointer to the
+ * first chunk of physical page addresses.
+ */
+struct kho_vmalloc {
+ DECLARE_KHOSER_PTR(first, struct kho_vmalloc_chunk *);
+ unsigned int total_pages;
+ unsigned short flags;
+ unsigned short order;
+};
+
#endif /* _LINUX_KHO_ABI_KEXEC_HANDOVER_H */
diff --git a/include/linux/kho/abi/memfd.h b/include/linux/kho/abi/memfd.h
index da7d063474a1..1af4c9dc5a06 100644
--- a/include/linux/kho/abi/memfd.h
+++ b/include/linux/kho/abi/memfd.h
@@ -12,7 +12,7 @@
#define _LINUX_KHO_ABI_MEMFD_H
#include <linux/types.h>
-#include <linux/kexec_handover.h>
+#include <linux/kho/abi/kexec_handover.h>
/**
* DOC: memfd Live Update ABI
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index d3d02a9ea391..a180b3367e8f 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -882,21 +882,6 @@ void kho_unpreserve_pages(struct page *page, unsigned int nr_pages)
}
EXPORT_SYMBOL_GPL(kho_unpreserve_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)
diff --git a/lib/test_kho.c b/lib/test_kho.c
index 47de56280795..3431daca6968 100644
--- a/lib/test_kho.c
+++ b/lib/test_kho.c
@@ -19,6 +19,7 @@
#include <linux/printk.h>
#include <linux/vmalloc.h>
#include <linux/kexec_handover.h>
+#include <linux/kho/abi/kexec_handover.h>
#include <net/checksum.h>
--
2.52.0.223.gf5cc29aaa4-goog
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