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 void load_fpu_regs(void); 51 void __load_fpu_regs(void); 52 53 static inline int test_fp_ctl(u32 fpc) 54 { 55 u32 orig_fpc; 56 int rc; 57 58 asm volatile( 59 " efpc %1\n" 60 " sfpc %2\n" 61 "0: sfpc %1\n" 62 " la %0,0\n" 63 "1:\n" 64 EX_TABLE(0b,1b) 65 : "=d" (rc), "=&d" (orig_fpc) 66 : "d" (fpc), "0" (-EINVAL)); 67 return rc; 68 } 69 70 #define KERNEL_FPC 1 71 #define KERNEL_VXR_V0V7 2 72 #define KERNEL_VXR_V8V15 4 73 #define KERNEL_VXR_V16V23 8 74 #define KERNEL_VXR_V24V31 16 75 76 #define KERNEL_VXR_LOW (KERNEL_VXR_V0V7|KERNEL_VXR_V8V15) 77 #define KERNEL_VXR_MID (KERNEL_VXR_V8V15|KERNEL_VXR_V16V23) 78 #define KERNEL_VXR_HIGH (KERNEL_VXR_V16V23|KERNEL_VXR_V24V31) 79 80 #define KERNEL_VXR (KERNEL_VXR_LOW|KERNEL_VXR_HIGH) 81 #define KERNEL_FPR (KERNEL_FPC|KERNEL_VXR_V0V7) 82 83 struct kernel_fpu; 84 85 /* 86 * Note the functions below must be called with preemption disabled. 87 * Do not enable preemption before calling __kernel_fpu_end() to prevent 88 * an corruption of an existing kernel FPU state. 89 * 90 * Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions. 91 */ 92 void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags); 93 void __kernel_fpu_end(struct kernel_fpu *state, u32 flags); 94 95 96 static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags) 97 { 98 preempt_disable(); 99 state->mask = S390_lowcore.fpu_flags; 100 if (!test_cpu_flag(CIF_FPU)) 101 /* Save user space FPU state and register contents */ 102 save_fpu_regs(); 103 else if (state->mask & flags) 104 /* Save FPU/vector register in-use by the kernel */ 105 __kernel_fpu_begin(state, flags); 106 S390_lowcore.fpu_flags |= flags; 107 } 108 109 static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags) 110 { 111 S390_lowcore.fpu_flags = state->mask; 112 if (state->mask & flags) 113 /* Restore FPU/vector register in-use by the kernel */ 114 __kernel_fpu_end(state, flags); 115 preempt_enable(); 116 } 117 118 #endif /* _ASM_S390_FPU_API_H */ 119