linux/arch/s390/include/asm/fpu/api.h
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   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
  49void save_fpu_regs(void);
  50void load_fpu_regs(void);
  51void __load_fpu_regs(void);
  52
  53static 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
  83struct 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 */
  92void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
  93void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
  94
  95
  96static 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
 109static 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