diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index da18172e50..272be0e79f 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2566,6 +2566,17 @@ guest will notify Xen that it has failed to acquire a spinlock.
 <major>, <minor> and <build> must be integers. The values will be
 encoded in guest CPUID 0x40000002 if viridian enlightenments are enabled.
 
+### vm-notify-window (Intel)
+> `= <integer>`
+
+> Default: `0`
+
+Specify the value of the VM Notify window used to detect locked VMs. Set to -1
+to disable the feature.  Value is in units of crystal clock cycles.
+
+Note the hardware might add a threshold to the provided value in order to make
+it safe, and hence using 0 is fine.
+
 ### vpid (Intel)
 > `= <boolean>`
 
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index d388e6729c..4985d25b85 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -67,6 +67,9 @@ integer_param("ple_gap", ple_gap);
 static unsigned int __read_mostly ple_window = 4096;
 integer_param("ple_window", ple_window);
 
+static unsigned int __ro_after_init vm_notify_window;
+integer_param("vm-notify-window", vm_notify_window);
+
 static bool __read_mostly opt_ept_pml = true;
 static s8 __read_mostly opt_ept_ad = -1;
 int8_t __read_mostly opt_ept_exec_sp = -1;
@@ -210,6 +213,7 @@ static void __init vmx_display_features(void)
     P(cpu_has_vmx_pml, "Page Modification Logging");
     P(cpu_has_vmx_tsc_scaling, "TSC Scaling");
     P(cpu_has_vmx_bus_lock_detection, "Bus Lock Detection");
+    P(cpu_has_vmx_notify_vm_exiting, "Notify VM Exit");
 #undef P
 
     if ( !printed )
@@ -329,6 +333,8 @@ static int vmx_init_vmcs_config(bool bsp)
             opt |= SECONDARY_EXEC_UNRESTRICTED_GUEST;
         if ( opt_ept_pml )
             opt |= SECONDARY_EXEC_ENABLE_PML;
+        if ( vm_notify_window != ~0u )
+            opt |= SECONDARY_EXEC_NOTIFY_VM_EXITING;
 
         /*
          * "APIC Register Virtualization" and "Virtual Interrupt Delivery"
@@ -1290,6 +1296,17 @@ static int construct_vmcs(struct vcpu *v)
     v->arch.hvm.vmx.exception_bitmap = HVM_TRAP_MASK
               | (paging_mode_hap(d) ? 0 : (1U << TRAP_page_fault))
               | (v->arch.fully_eager_fpu ? 0 : (1U << TRAP_no_device));
+    if ( cpu_has_vmx_notify_vm_exiting )
+    {
+        __vmwrite(NOTIFY_WINDOW, vm_notify_window);
+        /*
+         * Disable #AC and #DB interception: by using VM Notify Xen is
+         * guaranteed to get a VM exit even if the guest manages to lock the
+         * CPU.
+         */
+        v->arch.hvm.vmx.exception_bitmap &= ~((1U << TRAP_debug) |
+                                              (1U << TRAP_alignment_check));
+    }
     vmx_update_exception_bitmap(v);
 
     v->arch.hvm.guest_cr[0] = X86_CR0_PE | X86_CR0_ET;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index d69c02b00a..b372cde33e 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1419,10 +1419,19 @@ static void cf_check vmx_update_host_cr3(struct vcpu *v)
 
 void vmx_update_debug_state(struct vcpu *v)
 {
+    unsigned int mask = 1u << TRAP_int3;
+
+    if ( !cpu_has_monitor_trap_flag && cpu_has_vmx_notify_vm_exiting )
+        /*
+         * Only allow toggling TRAP_debug if notify VM exit is enabled, as
+         * unconditionally setting TRAP_debug is part of the XSA-156 fix.
+         */
+        mask |= 1u << TRAP_debug;
+
     if ( v->arch.hvm.debug_state_latch )
-        v->arch.hvm.vmx.exception_bitmap |= 1U << TRAP_int3;
+        v->arch.hvm.vmx.exception_bitmap |= mask;
     else
-        v->arch.hvm.vmx.exception_bitmap &= ~(1U << TRAP_int3);
+        v->arch.hvm.vmx.exception_bitmap &= ~mask;
 
     vmx_vmcs_enter(v);
     vmx_update_exception_bitmap(v);
@@ -4150,6 +4159,9 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         switch ( vector )
         {
         case TRAP_debug:
+            if ( cpu_has_monitor_trap_flag && cpu_has_vmx_notify_vm_exiting )
+                goto exit_and_crash;
+
             /*
              * Updates DR6 where debugger can peek (See 3B 23.2.1,
              * Table 23-1, "Exit Qualification for Debug Exceptions").
@@ -4589,6 +4601,22 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
          */
         break;
 
+    case EXIT_REASON_NOTIFY:
+        __vmread(EXIT_QUALIFICATION, &exit_qualification);
+
+        if ( exit_qualification & NOTIFY_VM_CONTEXT_INVALID )
+        {
+            perfc_incr(vmnotify_crash);
+            gprintk(XENLOG_ERR, "invalid VM context after notify vmexit\n");
+            domain_crash(v->domain);
+            break;
+        }
+
+        if ( unlikely(exit_qualification & INTR_INFO_NMI_UNBLOCKED_BY_IRET) )
+            undo_nmis_unblocked_by_iret();
+
+        break;
+
     case EXIT_REASON_VMX_PREEMPTION_TIMER_EXPIRED:
     case EXIT_REASON_INVPCID:
     /* fall through */
diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
index 5d3edc1642..0961eabf3f 100644
--- a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
+++ b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
@@ -267,6 +267,7 @@ extern u32 vmx_vmentry_control;
 #define SECONDARY_EXEC_XSAVES                   0x00100000
 #define SECONDARY_EXEC_TSC_SCALING              0x02000000
 #define SECONDARY_EXEC_BUS_LOCK_DETECTION       0x40000000
+#define SECONDARY_EXEC_NOTIFY_VM_EXITING        0x80000000
 extern u32 vmx_secondary_exec_control;
 
 #define VMX_EPT_EXEC_ONLY_SUPPORTED                         0x00000001
@@ -348,6 +349,8 @@ extern u64 vmx_ept_vpid_cap;
     (vmx_secondary_exec_control & SECONDARY_EXEC_TSC_SCALING)
 #define cpu_has_vmx_bus_lock_detection \
     (vmx_secondary_exec_control & SECONDARY_EXEC_BUS_LOCK_DETECTION)
+#define cpu_has_vmx_notify_vm_exiting \
+    (vmx_secondary_exec_control & SECONDARY_EXEC_NOTIFY_VM_EXITING)
 
 #define VMCS_RID_TYPE_MASK              0x80000000
 
@@ -455,6 +458,7 @@ enum vmcs_field {
     SECONDARY_VM_EXEC_CONTROL       = 0x0000401e,
     PLE_GAP                         = 0x00004020,
     PLE_WINDOW                      = 0x00004022,
+    NOTIFY_WINDOW                   = 0x00004024,
     VM_INSTRUCTION_ERROR            = 0x00004400,
     VM_EXIT_REASON                  = 0x00004402,
     VM_EXIT_INTR_INFO               = 0x00004404,
diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmx.h b/xen/arch/x86/include/asm/hvm/vmx/vmx.h
index bc0caad6fb..e429de8541 100644
--- a/xen/arch/x86/include/asm/hvm/vmx/vmx.h
+++ b/xen/arch/x86/include/asm/hvm/vmx/vmx.h
@@ -221,6 +221,7 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc)
 #define EXIT_REASON_XSAVES              63
 #define EXIT_REASON_XRSTORS             64
 #define EXIT_REASON_BUS_LOCK            74
+#define EXIT_REASON_NOTIFY              75
 /* Remember to also update VMX_PERF_EXIT_REASON_SIZE! */
 
 /*
@@ -236,6 +237,11 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc)
 #define INTR_INFO_VALID_MASK            0x80000000      /* 31 */
 #define INTR_INFO_RESVD_BITS_MASK       0x7ffff000
 
+/*
+ * Exit Qualifications for NOTIFY VM EXIT
+ */
+#define NOTIFY_VM_CONTEXT_INVALID       1u
+
 /*
  * Exit Qualifications for MOV for Control Register Access
  */
diff --git a/xen/arch/x86/include/asm/perfc_defn.h b/xen/arch/x86/include/asm/perfc_defn.h
index d6eb661940..a710fba8a8 100644
--- a/xen/arch/x86/include/asm/perfc_defn.h
+++ b/xen/arch/x86/include/asm/perfc_defn.h
@@ -6,7 +6,7 @@ PERFCOUNTER_ARRAY(exceptions,           "exceptions", 32)
 
 #ifdef CONFIG_HVM
 
-#define VMX_PERF_EXIT_REASON_SIZE 75
+#define VMX_PERF_EXIT_REASON_SIZE 76
 #define VMEXIT_NPF_PERFC 143
 #define SVM_PERF_EXIT_REASON_SIZE (VMEXIT_NPF_PERFC + 1)
 PERFCOUNTER_ARRAY(vmexits,              "vmexits",
@@ -126,5 +126,6 @@ PERFCOUNTER(realmode_exits,      "vmexits from realmode")
 PERFCOUNTER(pauseloop_exits, "vmexits from Pause-Loop Detection")
 
 PERFCOUNTER(buslock, "Bus Locks Detected")
+PERFCOUNTER(vmnotify_crash, "domain crashes by Notify VM Exit")
 
 /*#endif*/ /* __XEN_PERFC_DEFN_H__ */
