arch/arm64/include/asm/simd.h

   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  */
  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_irq() && !irqs_disabled() && !in_nmi() &&
  41                !this_cpu_read(fpsimd_context_busy);
  42 }
  43
  44 #else /* ! CONFIG_KERNEL_MODE_NEON */
  45
  46 static __must_check inline bool may_use_simd(void) {
  47         return false;
  48 }
  49
  50 #endif /* ! CONFIG_KERNEL_MODE_NEON */
  51
  52 #endif