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#include <asm/asm-extable.h>
49
50void save_fpu_regs(void);
51void load_fpu_regs(void);
52void __load_fpu_regs(void);
53
54static inline int test_fp_ctl(u32 fpc)
55{
56	u32 orig_fpc;
57	int rc;
58
59	asm volatile(
60		"	efpc    %1\n"
61		"	sfpc	%2\n"
62		"0:	sfpc	%1\n"
63		"	la	%0,0\n"
64		"1:\n"
65		EX_TABLE(0b,1b)
66		: "=d" (rc), "=&d" (orig_fpc)
67		: "d" (fpc), "0" (-EINVAL));
68	return rc;
69}
70
71#define KERNEL_FPC		1
72#define KERNEL_VXR_V0V7		2
73#define KERNEL_VXR_V8V15	4
74#define KERNEL_VXR_V16V23	8
75#define KERNEL_VXR_V24V31	16
76
77#define KERNEL_VXR_LOW		(KERNEL_VXR_V0V7|KERNEL_VXR_V8V15)
78#define KERNEL_VXR_MID		(KERNEL_VXR_V8V15|KERNEL_VXR_V16V23)
79#define KERNEL_VXR_HIGH		(KERNEL_VXR_V16V23|KERNEL_VXR_V24V31)
80
81#define KERNEL_VXR		(KERNEL_VXR_LOW|KERNEL_VXR_HIGH)
82#define KERNEL_FPR		(KERNEL_FPC|KERNEL_VXR_LOW)
83
84struct kernel_fpu;
85
86/*
87 * Note the functions below must be called with preemption disabled.
88 * Do not enable preemption before calling __kernel_fpu_end() to prevent
89 * an corruption of an existing kernel FPU state.
90 *
91 * Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
92 */
93void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
94void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
95
96
97static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
98{
99	preempt_disable();
100	state->mask = S390_lowcore.fpu_flags;
101	if (!test_cpu_flag(CIF_FPU))
102		/* Save user space FPU state and register contents */
103		save_fpu_regs();
104	else if (state->mask & flags)
105		/* Save FPU/vector register in-use by the kernel */
106		__kernel_fpu_begin(state, flags);
107	S390_lowcore.fpu_flags |= flags;
108}
109
110static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
111{
112	S390_lowcore.fpu_flags = state->mask;
113	if (state->mask & flags)
114		/* Restore FPU/vector register in-use by the kernel */
115		__kernel_fpu_end(state, flags);
116	preempt_enable();
117}
118
119#endif /* _ASM_S390_FPU_API_H */
120