1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * In-kernel FPU support functions
4 *
5 *
6 * Consider these guidelines before using in-kernel FPU functions:
7 *
8 * 1. Use kernel_fpu_begin() and kernel_fpu_end() to enclose all in-kernel
9 * use of floating-point or vector registers and instructions.
10 *
11 * 2. For kernel_fpu_begin(), specify the vector register range you want to
12 * use with the KERNEL_VXR_* constants. Consider these usage guidelines:
13 *
14 * a) If your function typically runs in process-context, use the lower
15 * half of the vector registers, for example, specify KERNEL_VXR_LOW.
16 * b) If your function typically runs in soft-irq or hard-irq context,
17 * prefer using the upper half of the vector registers, for example,
18 * specify KERNEL_VXR_HIGH.
19 *
20 * If you adhere to these guidelines, an interrupted process context
21 * does not require to save and restore vector registers because of
22 * disjoint register ranges.
23 *
24 * Also note that the __kernel_fpu_begin()/__kernel_fpu_end() functions
25 * includes logic to save and restore up to 16 vector registers at once.
26 *
27 * 3. You can nest kernel_fpu_begin()/kernel_fpu_end() by using different
28 * struct kernel_fpu states. Vector registers that are in use by outer
29 * levels are saved and restored. You can minimize the save and restore
30 * effort by choosing disjoint vector register ranges.
31 *
32 * 5. To use vector floating-point instructions, specify the KERNEL_FPC
33 * flag to save and restore floating-point controls in addition to any
34 * vector register range.
35 *
36 * 6. To use floating-point registers and instructions only, specify the
37 * KERNEL_FPR flag. This flag triggers a save and restore of vector
38 * registers V0 to V15 and floating-point controls.
39 *
40 * Copyright IBM Corp. 2015
41 * Author(s): Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
42 */
43
44 #ifndef _ASM_S390_FPU_API_H
45 #define _ASM_S390_FPU_API_H
46
47 #include <linux/preempt.h>
48
49 void save_fpu_regs(void);
50
51 static inline int test_fp_ctl(u32 fpc)
52 {
53 u32 orig_fpc;
54 int rc;
55
56 asm volatile(
57 " efpc %1\n"
58 " sfpc %2\n"
59 "0: sfpc %1\n"
60 " la %0,0\n"
61 "1:\n"
62 EX_TABLE(0b,1b)
63 : "=d" (rc), "=&d" (orig_fpc)
64 : "d" (fpc), "0" (-EINVAL));
65 return rc;
66 }
67
68 #define KERNEL_FPC 1
69 #define KERNEL_VXR_V0V7 2
70 #define KERNEL_VXR_V8V15 4
71 #define KERNEL_VXR_V16V23 8
72 #define KERNEL_VXR_V24V31 16
73
74 #define KERNEL_VXR_LOW (KERNEL_VXR_V0V7|KERNEL_VXR_V8V15)
75 #define KERNEL_VXR_MID (KERNEL_VXR_V8V15|KERNEL_VXR_V16V23)
76 #define KERNEL_VXR_HIGH (KERNEL_VXR_V16V23|KERNEL_VXR_V24V31)
77
78 #define KERNEL_VXR (KERNEL_VXR_LOW|KERNEL_VXR_HIGH)
79 #define KERNEL_FPR (KERNEL_FPC|KERNEL_VXR_V0V7)
80
81 struct kernel_fpu;
82
83 /*
84 * Note the functions below must be called with preemption disabled.
85 * Do not enable preemption before calling __kernel_fpu_end() to prevent
86 * an corruption of an existing kernel FPU state.
87 *
88 * Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
89 */
90 void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
91 void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
92
93
94 static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
95 {
96 preempt_disable();
97 state->mask = S390_lowcore.fpu_flags;
98 if (!test_cpu_flag(CIF_FPU))
99 /* Save user space FPU state and register contents */
100 save_fpu_regs();
101 else if (state->mask & flags)
102 /* Save FPU/vector register in-use by the kernel */
103 __kernel_fpu_begin(state, flags);
104 S390_lowcore.fpu_flags |= flags;
105 }
106
107 static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
108 {
109 S390_lowcore.fpu_flags = state->mask;
110 if (state->mask & flags)
111 /* Restore FPU/vector register in-use by the kernel */
112 __kernel_fpu_end(state, flags);
113 preempt_enable();
114 }
115
116 #endif /* _ASM_S390_FPU_API_H */