Messages in this thread Patch in this message | | | Date | Fri, 13 Mar 2015 10:47:08 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 1/4] x86/fpu: document user_fpu_begin() |
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On Wed, Mar 11, 2015 at 06:34:09PM +0100, Oleg Nesterov wrote: > Currently user_fpu_begin() has a single caller and it is not clear that > 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> > --- > arch/x86/include/asm/fpu-internal.h | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h > index 4bec98f..c615ae9 100644 > --- a/arch/x86/include/asm/fpu-internal.h > +++ b/arch/x86/include/asm/fpu-internal.h > @@ -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:
--- From: Oleg Nesterov <oleg@redhat.com> Date: Wed, 11 Mar 2015 18:34:09 +0100 Subject: [PATCH] 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> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Pekka Riikonen <priikone@iki.fi> Cc: Rik van Riel <riel@redhat.com> Cc: Suresh Siddha <sbsiddha@gmail.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Ingo Molnar <mingo@kernel.org> Link: http://lkml.kernel.org/r/20150311173409.GC5032@redhat.com Signed-off-by: --- arch/x86/include/asm/fpu-internal.h | 6 ++++-- 1 file 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..e8ee3da3b924 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) { -- -- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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