1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
4  */
5 
6 #ifndef __ASM_SIMD_H
7 #define __ASM_SIMD_H
8 
9 #include <linux/compiler.h>
10 #include <linux/irqflags.h>
11 #include <linux/percpu.h>
12 #include <linux/preempt.h>
13 #include <linux/types.h>
14 
15 DECLARE_PER_CPU(bool, fpsimd_context_busy);
16 
17 #ifdef CONFIG_KERNEL_MODE_NEON
18 
19 /*
20  * may_use_simd - whether it is allowable at this time to issue SIMD
21  *                instructions or access the SIMD register file
22  *
23  * Callers must not assume that the result remains true beyond the next
24  * preempt_enable() or return from softirq context.
25  */
may_use_simd(void)26 static __must_check inline bool may_use_simd(void)
27 {
28 	/*
29 	 * We must make sure that the SVE has been initialized properly
30 	 * before using the SIMD in kernel.
31 	 * fpsimd_context_busy is only set while preemption is disabled,
32 	 * and is clear whenever preemption is enabled. Since
33 	 * this_cpu_read() is atomic w.r.t. preemption, fpsimd_context_busy
34 	 * cannot change under our feet -- if it's set we cannot be
35 	 * migrated, and if it's clear we cannot be migrated to a CPU
36 	 * where it is set.
37 	 */
38 	return !WARN_ON(!system_capabilities_finalized()) &&
39 	       system_supports_fpsimd() &&
40 	       !in_hardirq() && !irqs_disabled() && !in_nmi() &&
41 	       !this_cpu_read(fpsimd_context_busy);
42 }
43 
44 #else /* ! CONFIG_KERNEL_MODE_NEON */
45 
may_use_simd(void)46 static __must_check inline bool may_use_simd(void) {
47 	return false;
48 }
49 
50 #endif /* ! CONFIG_KERNEL_MODE_NEON */
51 
52 #endif
53