1/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
2#ifndef _UAPI_LINUX_RSEQ_H
3#define _UAPI_LINUX_RSEQ_H
4
5/*
6 * linux/rseq.h
7 *
8 * Restartable sequences system call API
9 *
10 * Copyright (c) 2015-2018 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 */
12
13#include <linux/types.h>
14#include <asm/byteorder.h>
15
16enum rseq_cpu_id_state {
17 RSEQ_CPU_ID_UNINITIALIZED = -1,
18 RSEQ_CPU_ID_REGISTRATION_FAILED = -2,
19};
20
21enum rseq_flags {
22 RSEQ_FLAG_UNREGISTER = (1 << 0),
23};
24
25enum rseq_cs_flags_bit {
26 RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT_BIT = 0,
27 RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT = 1,
28 RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT = 2,
29};
30
31enum rseq_cs_flags {
32 RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT =
33 (1U << RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT_BIT),
34 RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL =
35 (1U << RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT),
36 RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE =
37 (1U << RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT),
38};
39
40/*
41 * struct rseq_cs is aligned on 4 * 8 bytes to ensure it is always
42 * contained within a single cache-line. It is usually declared as
43 * link-time constant data.
44 */
45struct rseq_cs {
46 /* Version of this structure. */
47 __u32 version;
48 /* enum rseq_cs_flags */
49 __u32 flags;
50 __u64 start_ip;
51 /* Offset from start_ip. */
52 __u64 post_commit_offset;
53 __u64 abort_ip;
54} __attribute__((aligned(4 * sizeof(__u64))));
55
56/*
57 * struct rseq is aligned on 4 * 8 bytes to ensure it is always
58 * contained within a single cache-line.
59 *
60 * A single struct rseq per thread is allowed.
61 */
62struct rseq {
63 /*
64 * Restartable sequences cpu_id_start field. Updated by the
65 * kernel. Read by user-space with single-copy atomicity
66 * semantics. This field should only be read by the thread which
67 * registered this data structure. Aligned on 32-bit. Always
68 * contains a value in the range of possible CPUs, although the
69 * value may not be the actual current CPU (e.g. if rseq is not
70 * initialized). This CPU number value should always be compared
71 * against the value of the cpu_id field before performing a rseq
72 * commit or returning a value read from a data structure indexed
73 * using the cpu_id_start value.
74 */
75 __u32 cpu_id_start;
76 /*
77 * Restartable sequences cpu_id field. Updated by the kernel.
78 * Read by user-space with single-copy atomicity semantics. This
79 * field should only be read by the thread which registered this
80 * data structure. Aligned on 32-bit. Values
81 * RSEQ_CPU_ID_UNINITIALIZED and RSEQ_CPU_ID_REGISTRATION_FAILED
82 * have a special semantic: the former means "rseq uninitialized",
83 * and latter means "rseq initialization failed". This value is
84 * meant to be read within rseq critical sections and compared
85 * with the cpu_id_start value previously read, before performing
86 * the commit instruction, or read and compared with the
87 * cpu_id_start value before returning a value loaded from a data
88 * structure indexed using the cpu_id_start value.
89 */
90 __u32 cpu_id;
91 /*
92 * Restartable sequences rseq_cs field.
93 *
94 * Contains NULL when no critical section is active for the current
95 * thread, or holds a pointer to the currently active struct rseq_cs.
96 *
97 * Updated by user-space, which sets the address of the currently
98 * active rseq_cs at the beginning of assembly instruction sequence
99 * block, and set to NULL by the kernel when it restarts an assembly
100 * instruction sequence block, as well as when the kernel detects that
101 * it is preempting or delivering a signal outside of the range
102 * targeted by the rseq_cs. Also needs to be set to NULL by user-space
103 * before reclaiming memory that contains the targeted struct rseq_cs.
104 *
105 * Read and set by the kernel. Set by user-space with single-copy
106 * atomicity semantics. This field should only be updated by the
107 * thread which registered this data structure. Aligned on 64-bit.
108 */
109 union {
110 __u64 ptr64;
111#ifdef __LP64__
112 __u64 ptr;
113#else
114 struct {
115#if (defined(__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) || defined(__BIG_ENDIAN)
116 __u32 padding; /* Initialized to zero. */
117 __u32 ptr32;
118#else /* LITTLE */
119 __u32 ptr32;
120 __u32 padding; /* Initialized to zero. */
121#endif /* ENDIAN */
122 } ptr;
123#endif
124 } rseq_cs;
125
126 /*
127 * Restartable sequences flags field.
128 *
129 * This field should only be updated by the thread which
130 * registered this data structure. Read by the kernel.
131 * Mainly used for single-stepping through rseq critical sections
132 * with debuggers.
133 *
134 * - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT
135 * Inhibit instruction sequence block restart on preemption
136 * for this thread.
137 * - RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL
138 * Inhibit instruction sequence block restart on signal
139 * delivery for this thread.
140 * - RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
141 * Inhibit instruction sequence block restart on migration for
142 * this thread.
143 */
144 __u32 flags;
145} __attribute__((aligned(4 * sizeof(__u64))));
146
147#endif /* _UAPI_LINUX_RSEQ_H */
148