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| author | Oleg Nesterov <oleg@redhat.com> | 2015-03-11 18:34:09 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-03-23 10:13:58 +0100 |
| commit | fb14b4eadf73500d3b2104f031472a268562c047 (patch) | |
| tree | e0c2e7fc48204f27e2f879a546ee0832c4a2027d /arch/x86/include/asm/fpu-internal.h | |
| parent | eda2360ad18b7cde87728fad85c6735a52c2576e (diff) | |
| download | linux-fb14b4eadf73500d3b2104f031472a268562c047.tar.gz linux-fb14b4eadf73500d3b2104f031472a268562c047.tar.bz2 linux-fb14b4eadf73500d3b2104f031472a268562c047.zip | |
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>
Diffstat (limited to 'arch/x86/include/asm/fpu-internal.h')
| -rw-r--r-- | arch/x86/include/asm/fpu-internal.h | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h index 810f20fd4e4e..c58c9302152b 100644 --- a/arch/x86/include/asm/fpu-internal.h +++ b/arch/x86/include/asm/fpu-internal.h @@ -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) { |