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i387.h
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1 /*
2  * Copyright (C) 1994 Linus Torvalds
3  *
4  * Pentium III FXSR, SSE support
5  * General FPU state handling cleanups
6  * Gareth Hughes <[email protected]>, 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 {
46 }
47 
48 static inline void kernel_fpu_end(void)
49 {
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 */