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/* SPDX-License-Identifier: GPL-2.0 */
* In-kernel FPU support functions
* Consider these guidelines before using in-kernel FPU functions:
* 1. Use kernel_fpu_begin() and kernel_fpu_end() to enclose all in-kernel
* use of floating-point or vector registers and instructions.
* 2. For kernel_fpu_begin(), specify the vector register range you want to
* use with the KERNEL_VXR_* constants. Consider these usage guidelines:
* a) If your function typically runs in process-context, use the lower
* half of the vector registers, for example, specify KERNEL_VXR_LOW.
* b) If your function typically runs in soft-irq or hard-irq context,
* prefer using the upper half of the vector registers, for example,
* specify KERNEL_VXR_HIGH.
* If you adhere to these guidelines, an interrupted process context
* does not require to save and restore vector registers because of
* disjoint register ranges.
* Also note that the __kernel_fpu_begin()/__kernel_fpu_end() functions
* includes logic to save and restore up to 16 vector registers at once.
* 3. You can nest kernel_fpu_begin()/kernel_fpu_end() by using different
* struct kernel_fpu states. Vector registers that are in use by outer
* levels are saved and restored. You can minimize the save and restore
* effort by choosing disjoint vector register ranges.
* 5. To use vector floating-point instructions, specify the KERNEL_FPC
* flag to save and restore floating-point controls in addition to any
* vector register range.
* 6. To use floating-point registers and instructions only, specify the
* KERNEL_FPR flag. This flag triggers a save and restore of vector
* registers V0 to V15 and floating-point controls.
* Copyright IBM Corp. 2015
* Author(s): Hendrik Brueckner <>
#ifndef _ASM_S390_FPU_API_H
#define _ASM_S390_FPU_API_H
#include <linux/preempt.h>
void save_fpu_regs(void);
void load_fpu_regs(void);
void __load_fpu_regs(void);
static inline int test_fp_ctl(u32 fpc)
u32 orig_fpc;
int rc;
asm volatile(
" efpc %1\n"
" sfpc %2\n"
"0: sfpc %1\n"
" la %0,0\n"
: "=d" (rc), "=&d" (orig_fpc)
: "d" (fpc), "0" (-EINVAL));
return rc;
#define KERNEL_FPC 1
#define KERNEL_VXR_V0V7 2
#define KERNEL_VXR_V8V15 4
#define KERNEL_VXR_V16V23 8
#define KERNEL_VXR_V24V31 16
struct kernel_fpu;
* Note the functions below must be called with preemption disabled.
* Do not enable preemption before calling __kernel_fpu_end() to prevent
* an corruption of an existing kernel FPU state.
* Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
state->mask = S390_lowcore.fpu_flags;
if (!test_cpu_flag(CIF_FPU))
/* Save user space FPU state and register contents */
else if (state->mask & flags)
/* Save FPU/vector register in-use by the kernel */
__kernel_fpu_begin(state, flags);
S390_lowcore.fpu_flags |= flags;
static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
S390_lowcore.fpu_flags = state->mask;
if (state->mask & flags)
/* Restore FPU/vector register in-use by the kernel */
__kernel_fpu_end(state, flags);
#endif /* _ASM_S390_FPU_API_H */