diff options
Diffstat (limited to 'arch/arm64/include/asm/simd.h')
| -rw-r--r-- | arch/arm64/include/asm/simd.h | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h index 96959b52afae..5a1a927b74a2 100644 --- a/arch/arm64/include/asm/simd.h +++ b/arch/arm64/include/asm/simd.h @@ -9,15 +9,46 @@ #ifndef __ASM_SIMD_H #define __ASM_SIMD_H +#include <linux/compiler.h> +#include <linux/percpu.h> +#include <linux/preempt.h> #include <linux/types.h> +#ifdef CONFIG_KERNEL_MODE_NEON + +DECLARE_PER_CPU(bool, kernel_neon_busy); + /* * may_use_simd - whether it is allowable at this time to issue SIMD * instructions or access the SIMD register file + * + * Callers must not assume that the result remains true beyond the next + * preempt_enable() or return from softirq context. */ static __must_check inline bool may_use_simd(void) { - return true; + /* + * The raw_cpu_read() is racy if called with preemption enabled. + * This is not a bug: kernel_neon_busy is only set when + * preemption is disabled, so we cannot migrate to another CPU + * while it is set, nor can we migrate to a CPU where it is set. + * So, if we find it clear on some CPU then we're guaranteed to + * find it clear on any CPU we could migrate to. + * + * If we are in between kernel_neon_begin()...kernel_neon_end(), + * the flag will be set, but preemption is also disabled, so we + * can't migrate to another CPU and spuriously see it become + * false. + */ + return !in_irq() && !in_nmi() && !raw_cpu_read(kernel_neon_busy); } +#else /* ! CONFIG_KERNEL_MODE_NEON */ + +static __must_check inline bool may_use_simd(void) { + return false; +} + +#endif /* ! CONFIG_KERNEL_MODE_NEON */ + #endif |