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 #include <asm/asm-extable.h>
49 #include <asm/fpu/internal.h>
50
51 void save_fpu_regs(void);
52 void load_fpu_regs(void);
53 void __load_fpu_regs(void);
54
55 /**
56 * sfpc_safe - Set floating point control register safely.
57 * @fpc: new value for floating point control register
58 *
59 * Set floating point control register. This may lead to an exception,
60 * since a saved value may have been modified by user space (ptrace,
61 * signal return, kvm registers) to an invalid value. In such a case
62 * set the floating point control register to zero.
63 */
sfpc_safe(u32 fpc)64 static inline void sfpc_safe(u32 fpc)
65 {
66 asm volatile("\n"
67 "0: sfpc %[fpc]\n"
68 "1: nopr %%r7\n"
69 ".pushsection .fixup, \"ax\"\n"
70 "2: lghi %[fpc],0\n"
71 " jg 0b\n"
72 ".popsection\n"
73 EX_TABLE(1b, 2b)
74 : [fpc] "+d" (fpc)
75 : : "memory");
76 }
77
78 #define KERNEL_FPC 1
79 #define KERNEL_VXR_V0V7 2
80 #define KERNEL_VXR_V8V15 4
81 #define KERNEL_VXR_V16V23 8
82 #define KERNEL_VXR_V24V31 16
83
84 #define KERNEL_VXR_LOW (KERNEL_VXR_V0V7|KERNEL_VXR_V8V15)
85 #define KERNEL_VXR_MID (KERNEL_VXR_V8V15|KERNEL_VXR_V16V23)
86 #define KERNEL_VXR_HIGH (KERNEL_VXR_V16V23|KERNEL_VXR_V24V31)
87
88 #define KERNEL_VXR (KERNEL_VXR_LOW|KERNEL_VXR_HIGH)
89 #define KERNEL_FPR (KERNEL_FPC|KERNEL_VXR_LOW)
90
91 struct kernel_fpu;
92
93 /*
94 * Note the functions below must be called with preemption disabled.
95 * Do not enable preemption before calling __kernel_fpu_end() to prevent
96 * an corruption of an existing kernel FPU state.
97 *
98 * Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
99 */
100 void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
101 void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
102
103
kernel_fpu_begin(struct kernel_fpu * state,u32 flags)104 static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
105 {
106 preempt_disable();
107 state->mask = S390_lowcore.fpu_flags;
108 if (!test_cpu_flag(CIF_FPU))
109 /* Save user space FPU state and register contents */
110 save_fpu_regs();
111 else if (state->mask & flags)
112 /* Save FPU/vector register in-use by the kernel */
113 __kernel_fpu_begin(state, flags);
114 S390_lowcore.fpu_flags |= flags;
115 }
116
kernel_fpu_end(struct kernel_fpu * state,u32 flags)117 static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
118 {
119 S390_lowcore.fpu_flags = state->mask;
120 if (state->mask & flags)
121 /* Restore FPU/vector register in-use by the kernel */
122 __kernel_fpu_end(state, flags);
123 preempt_enable();
124 }
125
126 #endif /* _ASM_S390_FPU_API_H */
127