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 */ 117