Messages in this thread | | | Date | Fri, 13 Mar 2015 15:34:49 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/4] x86/fpu: document user_fpu_begin() |
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On 03/13, Borislav Petkov wrote: > > On Wed, Mar 11, 2015 at 06:34:09PM +0100, Oleg Nesterov wrote: > > @@ -464,7 +464,9 @@ static inline int restore_xstate_sig(void __user *buf, int ia32_frame) > > * Need to be preemption-safe. > > * > > * NOTE! user_fpu_begin() must be used only immediately before restoring > > - * it. This function does not do any save/restore on their own. > > + * it. This function does not do any save/restore on its own. In a lazy > > + * fpu mode this is just optimization to avoid a dna fault, the task can > > + * lose FPU right after preempt_enable(). > > */ > > I cleaned it up a bit more, if you don't mind: ...
> /* > - * Need to be preemption-safe. > + * Needs to be preemption-safe. > * > * NOTE! user_fpu_begin() must be used only immediately before restoring > - * it. This function does not do any save/restore on their own. > + * the save state. It does not do any saving/restoring on its own. In > + * lazy FPU mode, it is just an optimization to avoid a #NM exception, > + * the task can lose the FPU right after preempt_enable(). > */
Thank!
Oleg.
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