From 8546c008924d5fd1724fa698eaa92b414bafd50d Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2012 10:25:45 -0800 Subject: i387: Uninline the generic FP helpers that we expose to kernel modules Instead of exporting the very low-level internals of the FPU state save/restore code (ie things like 'fpu_owner_task'), we should export the higher-level interfaces. Inlining these things is pointless anyway: sure, sometimes the end result is small, but while 'stts()' can result in just three x86 instructions, those are not cheap instructions (writing %cr0 is a serializing instruction and a very slow one at that). So the overhead of a function call is not noticeable, and we really don't want random modules mucking about with our internal state save logic anyway. So this unexports 'fpu_owner_task', and instead uninlines and exports the actual functions that modules can use: fpu_kernel_begin/end() and unlazy_fpu(). Signed-off-by: Linus Torvalds Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1202211339590.5354@i5.linux-foundation.org Signed-off-by: H. Peter Anvin --- arch/x86/kernel/i387.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) (limited to 'arch/x86/kernel/i387.c') diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 739d859..17b7549 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -32,6 +32,86 @@ # define user32_fxsr_struct user_fxsr_struct #endif +/* + * Were we in an interrupt that interrupted kernel mode? + * + * We can do a kernel_fpu_begin/end() pair *ONLY* if that + * pair does nothing at all: the thread must not have fpu (so + * that we don't try to save the FPU state), and TS must + * be set (so that the clts/stts pair does nothing that is + * visible in the interrupted kernel thread). + */ +static inline bool interrupted_kernel_fpu_idle(void) +{ + return !__thread_has_fpu(current) && + (read_cr0() & X86_CR0_TS); +} + +/* + * Were we in user mode (or vm86 mode) when we were + * interrupted? + * + * Doing kernel_fpu_begin/end() is ok if we are running + * in an interrupt context from user mode - we'll just + * save the FPU state as required. + */ +static inline bool interrupted_user_mode(void) +{ + struct pt_regs *regs = get_irq_regs(); + return regs && user_mode_vm(regs); +} + +/* + * Can we use the FPU in kernel mode with the + * whole "kernel_fpu_begin/end()" sequence? + * + * It's always ok in process context (ie "not interrupt") + * but it is sometimes ok even from an irq. + */ +bool irq_fpu_usable(void) +{ + return !in_interrupt() || + interrupted_user_mode() || + interrupted_kernel_fpu_idle(); +} +EXPORT_SYMBOL(irq_fpu_usable); + +void kernel_fpu_begin(void) +{ + struct task_struct *me = current; + + WARN_ON_ONCE(!irq_fpu_usable()); + preempt_disable(); + if (__thread_has_fpu(me)) { + __save_init_fpu(me); + __thread_clear_has_fpu(me); + /* We do 'stts()' in kernel_fpu_end() */ + } else { + percpu_write(fpu_owner_task, NULL); + clts(); + } +} +EXPORT_SYMBOL(kernel_fpu_begin); + +void kernel_fpu_end(void) +{ + stts(); + preempt_enable(); +} +EXPORT_SYMBOL(kernel_fpu_end); + +void unlazy_fpu(struct task_struct *tsk) +{ + preempt_disable(); + if (__thread_has_fpu(tsk)) { + __save_init_fpu(tsk); + __thread_fpu_end(tsk); + } else + tsk->fpu_counter = 0; + preempt_enable(); +} +EXPORT_SYMBOL(unlazy_fpu); + #ifdef CONFIG_MATH_EMULATION # define HAVE_HWFP (boot_cpu_data.hard_math) #else -- cgit v1.1