memfd.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2
 3/*
 4 * Copyright (c) 2025, Google LLC.
 5 * Pasha Tatashin <pasha.tatashin@soleen.com>
 6 *
 7 * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
 8 * Pratyush Yadav <ptyadav@amazon.de>
 9 */
10
11#ifndef _LINUX_KHO_ABI_MEMFD_H
12#define _LINUX_KHO_ABI_MEMFD_H
13
14#include <linux/types.h>
15#include <linux/kexec_handover.h>
16
17/**
18 * DOC: memfd Live Update ABI
19 *
20 * This header defines the ABI for preserving the state of a memfd across a
21 * kexec reboot using the LUO.
22 *
23 * The state is serialized into a packed structure `struct memfd_luo_ser`
24 * which is handed over to the next kernel via the KHO mechanism.
25 *
26 * This interface is a contract. Any modification to the structure layout
27 * constitutes a breaking change. Such changes require incrementing the
28 * version number in the MEMFD_LUO_FH_COMPATIBLE string.
29 */
30
31/**
32 * MEMFD_LUO_FOLIO_DIRTY - The folio is dirty.
33 *
34 * This flag indicates the folio contains data from user. A non-dirty folio is
35 * one that was allocated (say using fallocate(2)) but not written to.
36 */
37#define MEMFD_LUO_FOLIO_DIRTY		BIT(0)
38
39/**
40 * MEMFD_LUO_FOLIO_UPTODATE - The folio is up-to-date.
41 *
42 * An up-to-date folio has been zeroed out. shmem zeroes out folios on first
43 * use. This flag tracks which folios need zeroing.
44 */
45#define MEMFD_LUO_FOLIO_UPTODATE	BIT(1)
46
47/**
48 * struct memfd_luo_folio_ser - Serialized state of a single folio.
49 * @pfn:       The page frame number of the folio.
50 * @flags:     Flags to describe the state of the folio.
51 * @index:     The page offset (pgoff_t) of the folio within the original file.
52 */
53struct memfd_luo_folio_ser {
54	u64 pfn:52;
55	u64 flags:12;
56	u64 index;
57} __packed;
58
59/**
60 * struct memfd_luo_ser - Main serialization structure for a memfd.
61 * @pos:       The file's current position (f_pos).
62 * @size:      The total size of the file in bytes (i_size).
63 * @nr_folios: Number of folios in the folios array.
64 * @folios:    KHO vmalloc descriptor pointing to the array of
65 *             struct memfd_luo_folio_ser.
66 */
67struct memfd_luo_ser {
68	u64 pos;
69	u64 size;
70	u64 nr_folios;
71	struct kho_vmalloc folios;
72} __packed;
73
74/* The compatibility string for memfd file handler */
75#define MEMFD_LUO_FH_COMPATIBLE	"memfd-v1"
76
77#endif /* _LINUX_KHO_ABI_MEMFD_H */