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