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x86: Fix the NMI nesting comments 

Some of the comments for the nesting NMI algorithm were stale and
had some references to some prototypes that were first tried.

I also updated the comments to be a little easier to understand
the flow of the code. It definitely needs the documentation.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2012-02-24 15:55:13 -05:00 committed by Steven Rostedt
parent 6261091302
commit 79fb4ad63e
1 changed files with 8 additions and 6 deletions
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14
arch/x86/kernel/entry_64.S
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@ -1624,11 +1624,12 @@ first_nmi:
* | pt_regs |
* +-------------------------+
*
* The saved RIP is used to fix up the copied RIP that a nested
* NMI may zero out. The original stack frame and the temp storage
* The saved stack frame is used to fix up the copied stack frame
* that a nested NMI may change to make the interrupted NMI iret jump
* to the repeat_nmi. The original stack frame and the temp storage
* is also used by nested NMIs and can not be trusted on exit.
*/
/* Do not pop rdx, nested NMIs will corrupt it */
/* Do not pop rdx, nested NMIs will corrupt that part of the stack */
movq (%rsp), %rdx
CFI_RESTORE rdx
@ -1641,6 +1642,8 @@ first_nmi:
.endr
CFI_DEF_CFA_OFFSET SS+8-RIP
/* Everything up to here is safe from nested NMIs */
/*
* If there was a nested NMI, the first NMI's iret will return
* here. But NMIs are still enabled and we can take another
@ -1667,9 +1670,8 @@ end_repeat_nmi:
/*
* Everything below this point can be preempted by a nested
* NMI if the first NMI took an exception. Repeated NMIs
* caused by an exception and nested NMI will start here, and
* can still be preempted by another NMI.
* NMI if the first NMI took an exception and reset our iret stack
* so that we repeat another NMI.
*/
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
subq $ORIG_RAX-R15, %rsp