lkml.org 
[lkml]   [2015]   [Mar]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 1/4] x86/fpu: document user_fpu_begin()
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().
*/
static inline void user_fpu_begin(void)
{
--
1.5.5.1



\
 
 \ /
  Last update: 2015-03-11 19:01    [W:0.539 / U:0.628 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site