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hc
2024-01-03 2f7c68cb55ecb7331f2381deb497c27155f32faf 
 kernel/arch/x86/kernel/reboot.c
....@@ -528,33 +528,29 @@
528528 	}
529529 }
530530 
531
-static void vmxoff_nmi(int cpu, struct pt_regs *regs)
532
-{
533
-	cpu_emergency_vmxoff();
534
-}
531
+static inline void nmi_shootdown_cpus_on_restart(void);
535532 
536
-/* Use NMIs as IPIs to tell all CPUs to disable virtualization */
537
-static void emergency_vmx_disable_all(void)
533
+static void emergency_reboot_disable_virtualization(void)
538534 {
539535 	/* Just make sure we won't change CPUs while doing this */
540536 	local_irq_disable();
541537 
542538 	/*
543
-	 * Disable VMX on all CPUs before rebooting, otherwise we risk hanging
544
-	 * the machine, because the CPU blocks INIT when it's in VMX root.
539
+	 * Disable virtualization on all CPUs before rebooting to avoid hanging
540
+	 * the system, as VMX and SVM block INIT when running in the host.
545541 	 *
546542 	 * We can't take any locks and we may be on an inconsistent state, so
547
-	 * use NMIs as IPIs to tell the other CPUs to exit VMX root and halt.
543
+	 * use NMIs as IPIs to tell the other CPUs to disable VMX/SVM and halt.
548544 	 *
549
-	 * Do the NMI shootdown even if VMX if off on _this_ CPU, as that
550
-	 * doesn't prevent a different CPU from being in VMX root operation.
545
+	 * Do the NMI shootdown even if virtualization is off on _this_ CPU, as
546
+	 * other CPUs may have virtualization enabled.
551547 	 */
552
-	if (cpu_has_vmx()) {
553
-		/* Safely force _this_ CPU out of VMX root operation. */
554
-		__cpu_emergency_vmxoff();
548
+	if (cpu_has_vmx() || cpu_has_svm(NULL)) {
549
+		/* Safely force _this_ CPU out of VMX/SVM operation. */
550
+		cpu_emergency_disable_virtualization();
555551 
556
-		/* Halt and exit VMX root operation on the other CPUs. */
557
-		nmi_shootdown_cpus(vmxoff_nmi);
552
+		/* Disable VMX/SVM and halt on other CPUs. */
553
+		nmi_shootdown_cpus_on_restart();
558554 	}
559555 }
560556 
....@@ -590,7 +586,7 @@
590586 	unsigned short mode;
591587 
592588 	if (reboot_emergency)
593
-		emergency_vmx_disable_all();
589
+		emergency_reboot_disable_virtualization();
594590 
595591 	tboot_shutdown(TB_SHUTDOWN_REBOOT);
596592 
....@@ -795,6 +791,17 @@
795791 /* This is the CPU performing the emergency shutdown work. */
796792 int crashing_cpu = -1;
797793 
794
+/*
795
+ * Disable virtualization, i.e. VMX or SVM, to ensure INIT is recognized during
796
+ * reboot.  VMX blocks INIT if the CPU is post-VMXON, and SVM blocks INIT if
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+ * GIF=0, i.e. if the crash occurred between CLGI and STGI.
798
+ */
799
+void cpu_emergency_disable_virtualization(void)
800
+{
801
+	cpu_emergency_vmxoff();
802
+	cpu_emergency_svm_disable();
803
+}
804
+
798805 #if defined(CONFIG_SMP)
799806 
800807 static nmi_shootdown_cb shootdown_callback;
....@@ -817,7 +824,14 @@
817824 		return NMI_HANDLED;
818825 	local_irq_disable();
819826 
820
-	shootdown_callback(cpu, regs);
827
+	if (shootdown_callback)
828
+		shootdown_callback(cpu, regs);
829
+
830
+	/*
831
+	 * Prepare the CPU for reboot _after_ invoking the callback so that the
832
+	 * callback can safely use virtualization instructions, e.g. VMCLEAR.
833
+	 */
834
+	cpu_emergency_disable_virtualization();
821835 
822836 	atomic_dec(&waiting_for_crash_ipi);
823837 	/* Assume hlt works */
....@@ -828,17 +842,31 @@
828842 	return NMI_HANDLED;
829843 }
830844 
831
-/*
832
- * Halt all other CPUs, calling the specified function on each of them
845
+/**
846
+ * nmi_shootdown_cpus - Stop other CPUs via NMI
847
+ * @callback:	Optional callback to be invoked from the NMI handler
833848  *
834
- * This function can be used to halt all other CPUs on crash
835
- * or emergency reboot time. The function passed as parameter
836
- * will be called inside a NMI handler on all CPUs.
849
+ * The NMI handler on the remote CPUs invokes @callback, if not
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+ * NULL, first and then disables virtualization to ensure that
851
+ * INIT is recognized during reboot.
852
+ *
853
+ * nmi_shootdown_cpus() can only be invoked once. After the first
854
+ * invocation all other CPUs are stuck in crash_nmi_callback() and
855
+ * cannot respond to a second NMI.
837856  */
838857 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
839858 {
840859 	unsigned long msecs;
860
+
841861 	local_irq_disable();
862
+
863
+	/*
864
+	 * Avoid certain doom if a shootdown already occurred; re-registering
865
+	 * the NMI handler will cause list corruption, modifying the callback
866
+	 * will do who knows what, etc...
867
+	 */
868
+	if (WARN_ON_ONCE(crash_ipi_issued))
869
+		return;
842870 
843871 	/* Make a note of crashing cpu. Will be used in NMI callback. */
844872 	crashing_cpu = safe_smp_processor_id();
....@@ -867,7 +895,17 @@
867895 		msecs--;
868896 	}
869897 
870
-	/* Leave the nmi callback set */
898
+	/*
899
+	 * Leave the nmi callback set, shootdown is a one-time thing.  Clearing
900
+	 * the callback could result in a NULL pointer dereference if a CPU
901
+	 * (finally) responds after the timeout expires.
902
+	 */
903
+}
904
+
905
+static inline void nmi_shootdown_cpus_on_restart(void)
906
+{
907
+	if (!crash_ipi_issued)
908
+		nmi_shootdown_cpus(NULL);
871909 }
872910 
873911 /*
....@@ -897,6 +935,8 @@
897935 	/* No other CPUs to shoot down */
898936 }
899937 
938
+static inline void nmi_shootdown_cpus_on_restart(void) { }
939
+
900940 void run_crash_ipi_callback(struct pt_regs *regs)
901941 {
902942 }