Have the NMI handler call the C language trap() routine and directly

exit via 'doreti_exit'.

Since the NMI interrupt may be taken at any time, including when
the processor has masked external interrupts, it is not safe to
call ast() as is done for normal interrupts.

Approved by:	re (scottl)

1 files changed, 27 insertions, 2 deletions

diff --git a/sys/i386/i386/exception.s b/sys/i386/i386/exception.s
index 2e69ab8..6a45179 100644
--- a/sys/i386/i386/exception.s
+++ b/sys/i386/i386/exception.s
@@ -78,8 +78,6 @@ IDTVEC(div)
 	pushl $0; TRAP(T_DIVIDE)
 IDTVEC(dbg)
 	pushl $0; TRAP(T_TRCTRAP)
-IDTVEC(nmi)
-	pushl $0; TRAP(T_NMI)
 IDTVEC(bpt)
 	pushl $0; TRAP(T_BPTFLT)
 IDTVEC(ofl)
@@ -215,6 +213,33 @@ ENTRY(fork_trampoline)
 	MEXITCOUNT
 	jmp	doreti
 
+/*
+ * NMI handling is somewhat special: NMI interrupts may be taken at
+ * any time, including when the processor has turned off external
+ * interrupts by clearing EFLAGS.IF.  This means that the kernel's
+ * internal state could be inconsistent at the time of the interrupt,
+ * and it is not safe to call "ast()" as is done in the exit path
+ * for normal interrupts.
+ *
+ * The NMI handler therefore invokes the C language routine "trap()"
+ * and directly jumps to 'doreti_exit'.
+ */
+IDTVEC(nmi)
+	/* create a trap frame */
+	pushl	$0
+	pushl	$T_NMI
+	pushal
+	pushl	%ds
+	pushl	%es
+	pushl	%fs
+	movl	$KDSEL,%eax
+	movl	%eax,%ds
+	movl	%eax,%es
+	movl	$KPSEL,%eax
+	movl	%eax,%fs
+	FAKE_MCOUNT(TF_EIP(%esp))
+	call	trap
+	jmp	doreti_exit
 
 /*
  * To efficiently implement classification of trap and interrupt handlers