From 73c132c15da504789b924871e2491479a18e4f6a Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Thu, 16 May 2013 11:41:48 +0200 Subject: ARM: add support for kernel mode NEON In order to safely support the use of NEON instructions in kernel mode, some precautions need to be taken: - the userland context that may be present in the registers (even if the NEON/VFP is currently disabled) must be stored under the correct task (which may not be 'current' in the UP case), - to avoid having to keep track of additional vfpstates for the kernel side, disallow the use of NEON in interrupt context and run with preemption disabled, - after use, re-enable preemption and re-enable the lazy restore machinery by disabling the NEON/VFP unit. This patch adds the functions kernel_neon_begin() and kernel_neon_end() which take care of the above. It also adds the Kconfig symbol KERNEL_MODE_NEON to enable it. Signed-off-by: Ard Biesheuvel Acked-by: Nicolas Pitre --- arch/arm/vfp/vfpmodule.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) (limited to 'arch/arm/vfp') diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 7620831a0c66..52b8f40b1c73 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include @@ -668,6 +669,52 @@ void vfp_kmode_exception(void) pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n"); } +#ifdef CONFIG_KERNEL_MODE_NEON + +/* + * Kernel-side NEON support functions + */ +void kernel_neon_begin(void) +{ + struct thread_info *thread = current_thread_info(); + unsigned int cpu; + u32 fpexc; + + /* + * Kernel mode NEON is only allowed outside of interrupt context + * with preemption disabled. This will make sure that the kernel + * mode NEON register contents never need to be preserved. + */ + BUG_ON(in_interrupt()); + cpu = get_cpu(); + + fpexc = fmrx(FPEXC) | FPEXC_EN; + fmxr(FPEXC, fpexc); + + /* + * Save the userland NEON/VFP state. Under UP, + * the owner could be a task other than 'current' + */ + if (vfp_state_in_hw(cpu, thread)) + vfp_save_state(&thread->vfpstate, fpexc); +#ifndef CONFIG_SMP + else if (vfp_current_hw_state[cpu] != NULL) + vfp_save_state(vfp_current_hw_state[cpu], fpexc); +#endif + vfp_current_hw_state[cpu] = NULL; +} +EXPORT_SYMBOL(kernel_neon_begin); + +void kernel_neon_end(void) +{ + /* Disable the NEON/VFP unit. */ + fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN); + put_cpu(); +} +EXPORT_SYMBOL(kernel_neon_end); + +#endif /* CONFIG_KERNEL_MODE_NEON */ + /* * VFP support code initialisation. */ -- cgit v1.2.3