arch/s390/include/asm/fpu/api.h

   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 */