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);
50
51static 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_LOW)
80
81struct 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 */
90void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
91void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
92
93
94static 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
107static 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