Messages in this thread | | | Date | Thu, 15 Feb 2007 11:07:54 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [patch 09/14] syslets: x86, add move_user_context() method |
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On Thu, 15 Feb 2007, Ingo Molnar wrote:
> /* > + * Move user-space context from one kernel thread to another. > + * This includes registers and FPU state. Callers must make > + * sure that neither task is running user context at the moment: > + */ > +void > +move_user_context(struct task_struct *new_task, struct task_struct *old_task) > +{ > + struct pt_regs *old_regs = task_pt_regs(old_task); > + struct pt_regs *new_regs = task_pt_regs(new_task); > + union i387_union *tmp; > + > + *new_regs = *old_regs; > + /* > + * Flip around the FPU state too: > + */ > + tmp = new_task->thread.i387; > + new_task->thread.i387 = old_task->thread.i387; > + old_task->thread.i387 = tmp; > +}
Let's say that old_task ("prev" at the incoming schedule) has TS_USEDFPU set. Its context gets moved to the new_task (the one returning to userspace) *before* the __unlazy_fpu() done in __switch_to(). The __unlazy_fpu() at the following schedule will save the state to the old new_task context, and that fine as far as the going-to-sleep task goes. The next fault happening in new_task (return to userspace one) will reload a non up2date context (the one we got from old_task, but never hit by the __unlazy_fpu() flush). Right?
- Davide
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