---

yaml
---
r: 312403
b: refs/heads/master
c: 70fb74a
h: refs/heads/master
i:
  312401: 801ab68
  312399: 754be7f
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: c7d65a78fc18ed70353baeb7497ec71a7c775ac5
+refs/heads/master: 70fb74a5420f9caa3e001d65004e4b669124283e

trunk/arch/x86/kernel/nmi.c

@@ -395,13 +395,22 @@ static __kprobes void default_do_nmi(struct pt_regs *regs)
  * thus there is no race between the first check of state for NOT_RUNNING
  * and setting it to NMI_EXECUTING. The HW will prevent nested NMIs
  * at this point.
+ *
+ * In case the NMI takes a page fault, we need to save off the CR2
+ * because the NMI could have preempted another page fault and corrupt
+ * the CR2 that is about to be read. As nested NMIs must be restarted
+ * and they can not take breakpoints or page faults, the update of the
+ * CR2 must be done before converting the nmi state back to NOT_RUNNING.
+ * Otherwise, there would be a race of another nested NMI coming in
+ * after setting state to NOT_RUNNING but before updating the nmi_cr2.
  */
 enum nmi_states {
 	NMI_NOT_RUNNING = 0,
 	NMI_EXECUTING,
 	NMI_LATCHED,
 };
 static DEFINE_PER_CPU(enum nmi_states, nmi_state);
+static DEFINE_PER_CPU(unsigned long, nmi_cr2);
 
 #define nmi_nesting_preprocess(regs)					\
 	do {								\
@@ -410,11 +419,14 @@ static DEFINE_PER_CPU(enum nmi_states, nmi_state);
 			return;						\
 		}							\
 		this_cpu_write(nmi_state, NMI_EXECUTING);		\
+		this_cpu_write(nmi_cr2, read_cr2());			\
 	} while (0);							\
 	nmi_restart:
 
 #define nmi_nesting_postprocess()					\
 	do {								\
+		if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))	\
+			write_cr2(this_cpu_read(nmi_cr2));		\
 		if (this_cpu_dec_return(nmi_state))			\
 			goto nmi_restart;				\
 	} while (0)