Commit fb14b4ea authored Mar 11, 2015 by Oleg Nesterov Committed by Ingo Molnar Mar 23, 2015

x86/fpu: Document user_fpu_begin()



Currently, user_fpu_begin() has a single caller and it is not clear why
do we actually need it and why we should not worry about preemption
right after preempt_enable().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pekka Riikonen <priikone@iki.fi>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Link: http://lkml.kernel.org/r/20150311173409.GC5032@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent eda2360a

arch/x86/include/asm/fpu-internal.h

+4 −2

Original line number	Diff line number	Diff line
		@@ -508,10 +508,12 @@ static inline int restore_xstate_sig(void __user *buf, int ia32_frame)
		}

		/*
		* 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().
		*/
		static inline void user_fpu_begin(void)
		{