+++ /dev/null
-From 45d5a1683c04be28abdf5c04c27b1417e0374486 Mon Sep 17 00:00:00 2001
-From: Steven Rostedt <rostedt@goodmis.org>
-Date: Sun, 19 Feb 2012 16:43:37 -0500
-Subject: x86/nmi: Test saved %cs in NMI to determine nested NMI case
-
-From: Steven Rostedt <rostedt@goodmis.org>
-
-commit 45d5a1683c04be28abdf5c04c27b1417e0374486 upstream.
-
-Currently, the NMI handler tests if it is nested by checking the
-special variable saved on the stack (set during NMI handling)
-and whether the saved stack is the NMI stack as well (to prevent
-the race when the variable is set to zero).
-
-But userspace may set their %rsp to any value as long as they do
-not derefence it, and it may make it point to the NMI stack,
-which will prevent NMIs from triggering while the userspace app
-is running. (I tested this, and it is indeed the case)
-
-Add another check to determine nested NMIs by looking at the
-saved %cs (code segment register) and making sure that it is the
-kernel code segment.
-
-Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
-Cc: H. Peter Anvin <hpa@zytor.com>
-Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
-Cc: Linus Torvalds <torvalds@linux-foundation.org>
-Link: http://lkml.kernel.org/r/1329687817.1561.27.camel@acer.local.home
-Signed-off-by: Ingo Molnar <mingo@elte.hu>
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-
-diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
-index 3fe8239..debd851 100644
---- a/arch/x86/kernel/entry_64.S
-+++ b/arch/x86/kernel/entry_64.S
-@@ -1532,6 +1532,13 @@ ENTRY(nmi)
- pushq_cfi %rdx
-
- /*
-+ * If %cs was not the kernel segment, then the NMI triggered in user
-+ * space, which means it is definitely not nested.
-+ */
-+ cmp $__KERNEL_CS, 16(%rsp)
-+ jne first_nmi
-+
-+ /*
- * Check the special variable on the stack to see if NMIs are
- * executing.
- */