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 
16 enum rseq_cpu_id_state {
17 	RSEQ_CPU_ID_UNINITIALIZED		= -1,
18 	RSEQ_CPU_ID_REGISTRATION_FAILED		= -2,
19 };
20 
21 enum rseq_flags {
22 	RSEQ_FLAG_UNREGISTER = (1 << 0),
23 };
24 
25 enum 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 
31 enum 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  */
45 struct 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  */
62 struct 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 	 * 32-bit architectures should update the low order bits of the
110 	 * rseq_cs field, leaving the high order bits initialized to 0.
111 	 */
112 	__u64 rseq_cs;
113 
114 	/*
115 	 * Restartable sequences flags field.
116 	 *
117 	 * This field should only be updated by the thread which
118 	 * registered this data structure. Read by the kernel.
119 	 * Mainly used for single-stepping through rseq critical sections
120 	 * with debuggers.
121 	 *
122 	 * - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT
123 	 *     Inhibit instruction sequence block restart on preemption
124 	 *     for this thread.
125 	 * - RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL
126 	 *     Inhibit instruction sequence block restart on signal
127 	 *     delivery for this thread.
128 	 * - RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
129 	 *     Inhibit instruction sequence block restart on migration for
130 	 *     this thread.
131 	 */
132 	__u32 flags;
133 } __attribute__((aligned(4 * sizeof(__u64))));
134 
135 #endif /* _UAPI_LINUX_RSEQ_H */
136