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7575637ab2
math_state_restore() can race with kernel_fpu_begin() if irq comes right after __thread_fpu_begin(), __save_init_fpu() will overwrite fpu->state we are going to restore. Add 2 simple helpers, kernel_fpu_disable() and kernel_fpu_enable() which simply set/clear in_kernel_fpu, and change math_state_restore() to exclude kernel_fpu_begin() in between. Alternatively we could use local_irq_save/restore, but probably these new helpers can have more users. Perhaps they should disable/enable preemption themselves, in this case we can remove preempt_disable() in __restore_xstate_sig(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: matt.fleming@intel.com Cc: bp@suse.de Cc: pbonzini@redhat.com Cc: luto@amacapital.net Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Suresh Siddha <sbsiddha@gmail.com> Link: http://lkml.kernel.org/r/20150115192028.GD27332@redhat.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
109 lines
2.7 KiB
C
109 lines
2.7 KiB
C
/*
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* Copyright (C) 1994 Linus Torvalds
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*
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* Pentium III FXSR, SSE support
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* General FPU state handling cleanups
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* Gareth Hughes <gareth@valinux.com>, May 2000
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* x86-64 work by Andi Kleen 2002
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*/
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#ifndef _ASM_X86_I387_H
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#define _ASM_X86_I387_H
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#ifndef __ASSEMBLY__
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#include <linux/sched.h>
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#include <linux/hardirq.h>
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struct pt_regs;
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struct user_i387_struct;
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extern int init_fpu(struct task_struct *child);
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extern void fpu_finit(struct fpu *fpu);
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extern int dump_fpu(struct pt_regs *, struct user_i387_struct *);
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extern void math_state_restore(void);
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extern bool irq_fpu_usable(void);
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/*
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* Careful: __kernel_fpu_begin/end() must be called with preempt disabled
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* and they don't touch the preempt state on their own.
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* If you enable preemption after __kernel_fpu_begin(), preempt notifier
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* should call the __kernel_fpu_end() to prevent the kernel/user FPU
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* state from getting corrupted. KVM for example uses this model.
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*
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* All other cases use kernel_fpu_begin/end() which disable preemption
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* during kernel FPU usage.
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*/
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extern void __kernel_fpu_begin(void);
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extern void __kernel_fpu_end(void);
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static inline void kernel_fpu_begin(void)
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{
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preempt_disable();
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WARN_ON_ONCE(!irq_fpu_usable());
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__kernel_fpu_begin();
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}
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static inline void kernel_fpu_end(void)
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{
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__kernel_fpu_end();
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preempt_enable();
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}
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/* Must be called with preempt disabled */
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extern void kernel_fpu_disable(void);
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extern void kernel_fpu_enable(void);
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/*
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* Some instructions like VIA's padlock instructions generate a spurious
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* DNA fault but don't modify SSE registers. And these instructions
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* get used from interrupt context as well. To prevent these kernel instructions
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* in interrupt context interacting wrongly with other user/kernel fpu usage, we
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* should use them only in the context of irq_ts_save/restore()
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*/
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static inline int irq_ts_save(void)
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{
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/*
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* If in process context and not atomic, we can take a spurious DNA fault.
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* Otherwise, doing clts() in process context requires disabling preemption
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* or some heavy lifting like kernel_fpu_begin()
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*/
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if (!in_atomic())
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return 0;
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if (read_cr0() & X86_CR0_TS) {
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clts();
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return 1;
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}
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return 0;
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}
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static inline void irq_ts_restore(int TS_state)
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{
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if (TS_state)
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stts();
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}
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/*
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* The question "does this thread have fpu access?"
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* is slightly racy, since preemption could come in
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* and revoke it immediately after the test.
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*
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* However, even in that very unlikely scenario,
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* we can just assume we have FPU access - typically
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* to save the FP state - we'll just take a #NM
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* fault and get the FPU access back.
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*/
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static inline int user_has_fpu(void)
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{
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return current->thread.fpu.has_fpu;
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}
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extern void unlazy_fpu(struct task_struct *tsk);
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_X86_I387_H */
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