arch/x86/include/asm/i387.h

   1 /*
   2  * Copyright (C) 1994 Linus Torvalds
   3  *
   4  * Pentium III FXSR, SSE support
   5  * General FPU state handling cleanups
   6  *      Gareth Hughes <gareth@valinux.com>, May 2000
   7  * x86-64 work by Andi Kleen 2002
   8  */
   9
  10 #ifndef _ASM_X86_I387_H
  11 #define _ASM_X86_I387_H
  12
  13 #ifndef __ASSEMBLY__
  14
  15 #include <linux/sched.h>
  16 #include <linux/hardirq.h>
  17
  18 struct pt_regs;
  19 struct user_i387_struct;
  20
  21 extern int init_fpu(struct task_struct *child);
  22 extern void fpu_finit(struct fpu *fpu);
  23 extern int dump_fpu(struct pt_regs *, struct user_i387_struct *);
  24 extern void math_state_restore(void);
  25
  26 extern bool irq_fpu_usable(void);
  27
  28 /*
  29  * Careful: __kernel_fpu_begin/end() must be called with preempt disabled
  30  * and they don't touch the preempt state on their own.
  31  * If you enable preemption after __kernel_fpu_begin(), preempt notifier
  32  * should call the __kernel_fpu_end() to prevent the kernel/user FPU
  33  * state from getting corrupted. KVM for example uses this model.
  34  *
  35  * All other cases use kernel_fpu_begin/end() which disable preemption
  36  * during kernel FPU usage.
  37  */
  38 extern void __kernel_fpu_begin(void);
  39 extern void __kernel_fpu_end(void);
  40
  41 static inline void kernel_fpu_begin(void)
  42 {
  43         WARN_ON_ONCE(!irq_fpu_usable());
  44         preempt_disable();
  45         __kernel_fpu_begin();
  46 }
  47
  48 static inline void kernel_fpu_end(void)
  49 {
  50         __kernel_fpu_end();
  51         preempt_enable();
  52 }
  53
  54 /*
  55  * Some instructions like VIA's padlock instructions generate a spurious
  56  * DNA fault but don't modify SSE registers. And these instructions
  57  * get used from interrupt context as well. To prevent these kernel instructions
  58  * in interrupt context interacting wrongly with other user/kernel fpu usage, we
  59  * should use them only in the context of irq_ts_save/restore()
  60  */
  61 static inline int irq_ts_save(void)
  62 {
  63         /*
  64          * If in process context and not atomic, we can take a spurious DNA fault.
  65          * Otherwise, doing clts() in process context requires disabling preemption
  66          * or some heavy lifting like kernel_fpu_begin()
  67          */
  68         if (!in_atomic())
  69                 return 0;
  70
  71         if (read_cr0() & X86_CR0_TS) {
  72                 clts();
  73                 return 1;
  74         }
  75
  76         return 0;
  77 }
  78
  79 static inline void irq_ts_restore(int TS_state)
  80 {
  81         if (TS_state)
  82                 stts();
  83 }
  84
  85 /*
  86  * The question "does this thread have fpu access?"
  87  * is slightly racy, since preemption could come in
  88  * and revoke it immediately after the test.
  89  *
  90  * However, even in that very unlikely scenario,
  91  * we can just assume we have FPU access - typically
  92  * to save the FP state - we'll just take a #NM
  93  * fault and get the FPU access back.
  94  */
  95 static inline int user_has_fpu(void)
  96 {
  97         return current->thread.fpu.has_fpu;
  98 }
  99
 100 extern void unlazy_fpu(struct task_struct *tsk);
 101
 102 #endif /* __ASSEMBLY__ */
 103
 104 #endif /* _ASM_X86_I387_H */