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x86: Document the NMI handler about not using paranoid_exit 

Linus cleaned up the NMI handler but it still needs some comments to
explain why it uses save_paranoid but not paranoid_exit. Just to keep
others from adding that in the future, document why it's not used.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2011-12-08 12:32:27 -05:00 committed by Steven Rostedt
parent 549c89b98c
commit 1fd466efc8
1 changed files with 8 additions and 1 deletions
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9
arch/x86/kernel/entry_64.S
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@ -1480,9 +1480,16 @@ END(error_exit)
ENTRY(nmi)
INTR_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
pushq_cfi $-1
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
subq $ORIG_RAX-R15, %rsp
CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
/*
* Use save_paranoid to handle SWAPGS, but no need to use paranoid_exit
* as we should not be calling schedule in NMI context.
* Even with normal interrupts enabled. An NMI should not be
* setting NEED_RESCHED or anything that normal interrupts and
* exceptions might do.
*/
call save_paranoid
DEFAULT_FRAME 0
/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */