kgdb,i386: Fix corner case access to sp with NMI watch dog exception

It is possible for the user_mode_vm(regs) check to return true for a
non master kgdb cpu or when the master kgdb cpu handles the NMI watch
dog exception.

The solution is simply to select the correct stack pointer location
based on the check to user_mode_vm(regs).
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

arch/x86/kernel/kgdb.c

@@ -85,10 +85,15 @@ void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
 	gdb_regs[GDB_DS]	= regs->ds;
 	gdb_regs[GDB_ES]	= regs->es;
 	gdb_regs[GDB_CS]	= regs->cs;
-	gdb_regs[GDB_SS]	= __KERNEL_DS;
 	gdb_regs[GDB_FS]	= 0xFFFF;
 	gdb_regs[GDB_GS]	= 0xFFFF;
-	gdb_regs[GDB_SP]	= (int)&regs->sp;
+	if (user_mode_vm(regs)) {
+		gdb_regs[GDB_SS] = regs->ss;
+		gdb_regs[GDB_SP] = regs->sp;
+	} else {
+		gdb_regs[GDB_SS] = __KERNEL_DS;
+		gdb_regs[GDB_SP] = (unsigned long)&regs->sp;
+	}
 #else
 	gdb_regs[GDB_R8]	= regs->r8;
 	gdb_regs[GDB_R9]	= regs->r9;