x86/HVM: allow per-domain usage of hardware virtualized APIC

Introduce a new per-domain creation x86 specific flag to
select whether hardware assisted virtualization should be used for
x{2}APIC.

A per-domain option is added to xl in order to select the usage of
x{2}APIC hardware assisted virtualization, as well as a global
configuration option.

Having all APIC interaction exit to Xen for emulation is slow and can
induce much overhead. Hardware can speed up x{2}APIC by decoding the
APIC access and providing a VM exit with a more specific exit reason
than a regular EPT fault or by altogether avoiding a VM exit.

On the other hand, being able to disable x{2}APIC hardware assisted
virtualization can be useful for testing and debugging purposes.

Note:

- vmx_install_vlapic_mapping doesn't require modifications regardless
of whether the guest has "Virtualize APIC accesses" enabled or not,
i.e., setting the APIC_ACCESS_ADDR VMCS field is fine so long as
virtualize_apic_accesses is supported by the CPU.

- Both per-domain and global assisted_x{2}apic options are not part of
the migration stream, unless explicitly set in the respective
configuration files. Default settings of assisted_x{2}apic done
internally by the toolstack, based on host capabilities at create
time, are not migrated.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jane Malalane <jane.malalane@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Reviewed-by: "Roger Pau Monné" <roger.pau@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

docs/man/xl.cfg.5.pod.in

@@ -1862,6 +1862,21 @@ firmware tables when using certain older guest Operating
 Systems. These tables have been superseded by newer constructs within
 the ACPI tables.
 
+=item B<assisted_xapic=BOOLEAN>
+
+B<(x86 only)> Enables or disables hardware assisted virtualization for
+xAPIC. With this option enabled, a memory-mapped APIC access will be
+decoded by hardware and either issue a more specific VM exit than just
+a p2m fault, or altogether avoid a VM exit. The
+default is settable via L<xl.conf(5)>.
+
+=item B<assisted_x2apic=BOOLEAN>
+
+B<(x86 only)> Enables or disables hardware assisted virtualization for
+x2APIC. With this option enabled, certain accesses to MSR APIC
+registers will avoid a VM exit into the hypervisor. The default is
+settable via L<xl.conf(5)>.
+
 =item B<nx=BOOLEAN>
 
 B<(x86 only)> Hides or exposes the No-eXecute capability. This allows a guest

docs/man/xl.conf.5.pod.in

@@ -107,6 +107,18 @@ Sets the default value for the C<max_grant_version> domain config value.
 
 Default: maximum grant version supported by the hypervisor.
 
+=item B<assisted_xapic=BOOLEAN>
+
+If enabled, domains will use xAPIC hardware assisted virtualization by default.
+
+Default: enabled if supported.
+
+=item B<assisted_x2apic=BOOLEAN>
+
+If enabled, domains will use x2APIC hardware assisted virtualization by default.
+
+Default: enabled if supported.
+
 =item B<vif.default.script="PATH">
 
 Configures the default hotplug script used by virtual network devices.

tools/golang/xenlight/helpers.gen.go

@@ -1120,6 +1120,12 @@ x.ArchArm.Vuart = VuartType(xc.arch_arm.vuart)
 if err := x.ArchX86.MsrRelaxed.fromC(&xc.arch_x86.msr_relaxed);err != nil {
 return fmt.Errorf("converting field ArchX86.MsrRelaxed: %v", err)
 }
+if err := x.ArchX86.AssistedXapic.fromC(&xc.arch_x86.assisted_xapic);err != nil {
+return fmt.Errorf("converting field ArchX86.AssistedXapic: %v", err)
+}
+if err := x.ArchX86.AssistedX2Apic.fromC(&xc.arch_x86.assisted_x2apic);err != nil {
+return fmt.Errorf("converting field ArchX86.AssistedX2Apic: %v", err)
+}
 x.Altp2M = Altp2MMode(xc.altp2m)
 x.VmtraceBufKb = int(xc.vmtrace_buf_kb)
 if err := x.Vpmu.fromC(&xc.vpmu);err != nil {
@@ -1605,6 +1611,12 @@ xc.arch_arm.vuart = C.libxl_vuart_type(x.ArchArm.Vuart)
 if err := x.ArchX86.MsrRelaxed.toC(&xc.arch_x86.msr_relaxed); err != nil {
 return fmt.Errorf("converting field ArchX86.MsrRelaxed: %v", err)
 }
+if err := x.ArchX86.AssistedXapic.toC(&xc.arch_x86.assisted_xapic); err != nil {
+return fmt.Errorf("converting field ArchX86.AssistedXapic: %v", err)
+}
+if err := x.ArchX86.AssistedX2Apic.toC(&xc.arch_x86.assisted_x2apic); err != nil {
+return fmt.Errorf("converting field ArchX86.AssistedX2Apic: %v", err)
+}
 xc.altp2m = C.libxl_altp2m_mode(x.Altp2M)
 xc.vmtrace_buf_kb = C.int(x.VmtraceBufKb)
 if err := x.Vpmu.toC(&xc.vpmu); err != nil {

tools/golang/xenlight/types.gen.go

@@ -520,6 +520,8 @@ Vuart VuartType
 }
 ArchX86 struct {
 MsrRelaxed Defbool
+AssistedXapic Defbool
+AssistedX2Apic Defbool
 }
 Altp2M Altp2MMode
 VmtraceBufKb int

tools/include/libxl.h

@@ -542,6 +542,13 @@
  */
 #define LIBXL_HAVE_PHYSINFO_ASSISTED_APIC 1
 
+/*
+ * LIBXL_HAVE_ASSISTED_APIC indicates that libxl_domain_build_info has
+ * assisted_xapic and assisted_x2apic fields for enabling hardware
+ * assisted virtualization for x{2}apic per domain.
+ */
+#define LIBXL_HAVE_ASSISTED_APIC 1
+
 /*
  * libxl ABI compatibility
  *

tools/libs/light/libxl_arch.h

@@ -71,8 +71,9 @@ void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
                                                libxl_domain_create_info *c_info);
 
 _hidden
-void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
-                                              libxl_domain_build_info *b_info);
+int libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
+                                             libxl_domain_build_info *b_info,
+                                             const libxl_physinfo *physinfo);
 
 _hidden
 int libxl__arch_passthrough_mode_setdefault(libxl__gc *gc,

tools/libs/light/libxl_arm.c

@@ -1384,14 +1384,15 @@ void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
     }
 }
 
-void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
-                                              libxl_domain_build_info *b_info)
+int libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
+                                             libxl_domain_build_info *b_info,
+                                             const libxl_physinfo *physinfo)
 {
     /* ACPI is disabled by default */
     libxl_defbool_setdefault(&b_info->acpi, false);
 
     if (b_info->type != LIBXL_DOMAIN_TYPE_PV)
-        return;
+        return 0;
 
     LOG(DEBUG, "Converting build_info to PVH");
 
@@ -1399,6 +1400,8 @@ void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
     memset(&b_info->u, '\0', sizeof(b_info->u));
     b_info->type = LIBXL_DOMAIN_TYPE_INVALID;
     libxl_domain_build_info_init_type(b_info, LIBXL_DOMAIN_TYPE_PVH);
+
+    return 0;
 }
 
 int libxl__arch_passthrough_mode_setdefault(libxl__gc *gc,

tools/libs/light/libxl_create.c

@@ -75,6 +75,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
                                         libxl_domain_build_info *b_info)
 {
     int i, rc;
+    libxl_physinfo info;
 
     if (b_info->type != LIBXL_DOMAIN_TYPE_HVM &&
         b_info->type != LIBXL_DOMAIN_TYPE_PV &&
@@ -264,7 +265,18 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
     if (!b_info->event_channels)
         b_info->event_channels = 1023;
 
-    libxl__arch_domain_build_info_setdefault(gc, b_info);
+    rc = libxl_get_physinfo(CTX, &info);
+    if (rc) {
+        LOG(ERROR, "failed to get hypervisor info");
+        return rc;
+    }
+
+    rc = libxl__arch_domain_build_info_setdefault(gc, b_info, &info);
+    if (rc) {
+        LOG(ERROR, "unable to set domain arch build info defaults");
+        return rc;
+    }
+
     libxl_defbool_setdefault(&b_info->dm_restrict, false);
 
     if (b_info->iommu_memkb == LIBXL_MEMKB_DEFAULT)
@@ -457,14 +469,6 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
     }
 
     if (b_info->max_grant_version == LIBXL_MAX_GRANT_DEFAULT) {
-        libxl_physinfo info;
-
-        rc = libxl_get_physinfo(CTX, &info);
-        if (rc) {
-            LOG(ERROR, "failed to get hypervisor info");
-            return rc;
-        }
-
         if (info.cap_gnttab_v2)
             b_info->max_grant_version = 2;
         else if (info.cap_gnttab_v1)

tools/libs/light/libxl_types.idl

@@ -648,6 +648,8 @@ libxl_domain_build_info = Struct("domain_build_info",[
                                ("vuart", libxl_vuart_type),
                               ])),
     ("arch_x86", Struct(None, [("msr_relaxed", libxl_defbool),
+                               ("assisted_xapic", libxl_defbool),
+                               ("assisted_x2apic", libxl_defbool),
                               ])),
     # Alternate p2m is not bound to any architecture or guest type, as it is
     # supported by x86 HVM and ARM support is planned.

tools/libs/light/libxl_x86.c

@@ -23,6 +23,15 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
     if (libxl_defbool_val(d_config->b_info.arch_x86.msr_relaxed))
         config->arch.misc_flags |= XEN_X86_MSR_RELAXED;
 
+    if (d_config->c_info.type != LIBXL_DOMAIN_TYPE_PV)
+    {
+        if (libxl_defbool_val(d_config->b_info.arch_x86.assisted_xapic))
+            config->arch.misc_flags |= XEN_X86_ASSISTED_XAPIC;
+
+        if (libxl_defbool_val(d_config->b_info.arch_x86.assisted_x2apic))
+            config->arch.misc_flags |= XEN_X86_ASSISTED_X2APIC;
+    }
+
     return 0;
 }
 
@@ -819,11 +828,26 @@ void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
 {
 }
 
-void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
-                                              libxl_domain_build_info *b_info)
+int libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
+                                             libxl_domain_build_info *b_info,
+                                             const libxl_physinfo *physinfo)
 {
     libxl_defbool_setdefault(&b_info->acpi, true);
     libxl_defbool_setdefault(&b_info->arch_x86.msr_relaxed, false);
+
+    if (b_info->type != LIBXL_DOMAIN_TYPE_PV) {
+        libxl_defbool_setdefault(&b_info->arch_x86.assisted_xapic,
+                                 physinfo->cap_assisted_xapic);
+        libxl_defbool_setdefault(&b_info->arch_x86.assisted_x2apic,
+                                 physinfo->cap_assisted_x2apic);
+    }
+    else if (!libxl_defbool_is_default(b_info->arch_x86.assisted_xapic) ||
+             !libxl_defbool_is_default(b_info->arch_x86.assisted_x2apic)) {
+        LOG(ERROR, "Interrupt Controller Virtualization not supported for PV");
+        return ERROR_INVAL;
+    }
+
+    return 0;
 }
 
 int libxl__arch_passthrough_mode_setdefault(libxl__gc *gc,

tools/ocaml/libs/xc/xenctrl.ml

@@ -50,6 +50,8 @@ type x86_arch_emulation_flags =
 
 type x86_arch_misc_flags =
 	| X86_MSR_RELAXED
+	| X86_ASSISTED_XAPIC
+	| X86_ASSISTED_X2APIC
 
 type xen_x86_arch_domainconfig =
 {

tools/ocaml/libs/xc/xenctrl.mli

@@ -44,6 +44,8 @@ type x86_arch_emulation_flags =
 
 type x86_arch_misc_flags =
   | X86_MSR_RELAXED
+  | X86_ASSISTED_XAPIC
+  | X86_ASSISTED_X2APIC
 
 type xen_x86_arch_domainconfig = {
   emulation_flags: x86_arch_emulation_flags list;

tools/ocaml/libs/xc/xenctrl_stubs.c

@@ -244,7 +244,7 @@ CAMLprim value stub_xc_domain_create(value xch, value wanted_domid, value config
 
 		cfg.arch.misc_flags = ocaml_list_to_c_bitmap
 			/* ! x86_arch_misc_flags X86_ none */
-			/* ! XEN_X86_ XEN_X86_MSR_RELAXED all */
+			/* ! XEN_X86_ XEN_X86_MISC_FLAGS_MAX max */
 			(VAL_MISC_FLAGS);
 
 #undef VAL_MISC_FLAGS

tools/xl/xl.c

@@ -57,6 +57,8 @@ int max_grant_frames = -1;
 int max_maptrack_frames = -1;
 int max_grant_version = LIBXL_MAX_GRANT_DEFAULT;
 libxl_domid domid_policy = INVALID_DOMID;
+int assisted_xapic = -1;
+int assisted_x2apic = -1;
 
 xentoollog_level minmsglevel = minmsglevel_default;
 
@@ -201,6 +203,12 @@ static void parse_global_config(const char *configfile,
     if (!xlu_cfg_get_long (config, "claim_mode", &l, 0))
         claim_mode = l;
 
+    if (!xlu_cfg_get_long (config, "assisted_xapic", &l, 0))
+        assisted_xapic = l;
+
+    if (!xlu_cfg_get_long (config, "assisted_x2apic", &l, 0))
+        assisted_x2apic = l;
+
     xlu_cfg_replace_string (config, "remus.default.netbufscript",
         &default_remus_netbufscript, 0);
     xlu_cfg_replace_string (config, "colo.default.proxyscript",

tools/xl/xl.h

@@ -286,6 +286,8 @@ extern libxl_bitmap global_vm_affinity_mask;
 extern libxl_bitmap global_hvm_affinity_mask;
 extern libxl_bitmap global_pv_affinity_mask;
 extern libxl_domid domid_policy;
+extern int assisted_xapic;
+extern int assisted_x2apic;
 
 enum output_format {
     OUTPUT_FORMAT_JSON,

tools/xl/xl_parse.c

@@ -2765,6 +2765,25 @@ skip_usbdev:
 
     xlu_cfg_get_defbool(config, "vpmu", &b_info->vpmu, 0);
 
+    if (b_info->type != LIBXL_DOMAIN_TYPE_PV) {
+        e = xlu_cfg_get_long(config, "assisted_xapic", &l , 0);
+        if (!e)
+            libxl_defbool_set(&b_info->arch_x86.assisted_xapic, l);
+        else if (e != ESRCH)
+            exit(1);
+        else if (assisted_xapic != -1) /* use global default if present */
+            libxl_defbool_set(&b_info->arch_x86.assisted_xapic, assisted_xapic);
+
+        e = xlu_cfg_get_long(config, "assisted_x2apic", &l, 0);
+        if (!e)
+            libxl_defbool_set(&b_info->arch_x86.assisted_x2apic, l);
+        else if (e != ESRCH)
+            exit(1);
+        else if (assisted_x2apic != -1) /* use global default if present */
+            libxl_defbool_set(&b_info->arch_x86.assisted_x2apic,
+                              assisted_x2apic);
+    }
+
     xlu_cfg_destroy(config);
 }
 

xen/arch/x86/domain.c

@@ -50,6 +50,7 @@
 #include <asm/cpuidle.h>
 #include <asm/mpspec.h>
 #include <asm/ldt.h>
+#include <asm/hvm/domain.h>
 #include <asm/hvm/hvm.h>
 #include <asm/hvm/nestedhvm.h>
 #include <asm/hvm/support.h>
@@ -619,6 +620,8 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
     bool hvm = config->flags & XEN_DOMCTL_CDF_hvm;
     bool hap = config->flags & XEN_DOMCTL_CDF_hap;
     bool nested_virt = config->flags & XEN_DOMCTL_CDF_nested_virt;
+    bool assisted_xapic = config->arch.misc_flags & XEN_X86_ASSISTED_XAPIC;
+    bool assisted_x2apic = config->arch.misc_flags & XEN_X86_ASSISTED_X2APIC;
     unsigned int max_vcpus;
 
     if ( hvm ? !hvm_enabled : !IS_ENABLED(CONFIG_PV) )
@@ -685,13 +688,31 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
         }
     }
 
-    if ( config->arch.misc_flags & ~XEN_X86_MSR_RELAXED )
+    if ( config->arch.misc_flags & ~(XEN_X86_MSR_RELAXED |
+                                     XEN_X86_ASSISTED_XAPIC |
+                                     XEN_X86_ASSISTED_X2APIC) )
     {
         dprintk(XENLOG_INFO, "Invalid arch misc flags %#x\n",
                 config->arch.misc_flags);
         return -EINVAL;
     }
 
+    if ( (assisted_xapic || assisted_x2apic) && !hvm )
+    {
+        dprintk(XENLOG_INFO,
+                "Interrupt Controller Virtualization not supported for PV\n");
+        return -EINVAL;
+    }
+
+    if ( (assisted_xapic && !assisted_xapic_available) ||
+         (assisted_x2apic && !assisted_x2apic_available) )
+    {
+        dprintk(XENLOG_INFO,
+                "Hardware assisted x%sAPIC requested but not available\n",
+                assisted_xapic && !assisted_xapic_available ? "" : "2");
+        return -ENODEV;
+    }
+
     return 0;
 }
 
@@ -864,6 +885,12 @@ int arch_domain_create(struct domain *d,
 
     d->arch.msr_relaxed = config->arch.misc_flags & XEN_X86_MSR_RELAXED;
 
+    d->arch.hvm.assisted_xapic =
+        config->arch.misc_flags & XEN_X86_ASSISTED_XAPIC;
+
+    d->arch.hvm.assisted_x2apic =
+        config->arch.misc_flags & XEN_X86_ASSISTED_X2APIC;
+
     spec_ctrl_init_domain(d);
 
     return 0;

xen/arch/x86/hvm/vmx/vmcs.c

@@ -1134,6 +1134,10 @@ static int construct_vmcs(struct vcpu *v)
         __vmwrite(PLE_WINDOW, ple_window);
     }
 
+    if ( !has_assisted_xapic(d) )
+        v->arch.hvm.vmx.secondary_exec_control &=
+            ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+
     if ( cpu_has_vmx_secondary_exec_control )
         __vmwrite(SECONDARY_VM_EXEC_CONTROL,
                   v->arch.hvm.vmx.secondary_exec_control);

xen/arch/x86/hvm/vmx/vmx.c

@@ -3376,16 +3376,11 @@ static void vmx_install_vlapic_mapping(struct vcpu *v)
 
 void vmx_vlapic_msr_changed(struct vcpu *v)
 {
-    int virtualize_x2apic_mode;
     struct vlapic *vlapic = vcpu_vlapic(v);
     unsigned int msr;
 
-    virtualize_x2apic_mode = ( (cpu_has_vmx_apic_reg_virt ||
-                                cpu_has_vmx_virtual_intr_delivery) &&
-                               cpu_has_vmx_virtualize_x2apic_mode );
-
-    if ( !cpu_has_vmx_virtualize_apic_accesses &&
-         !virtualize_x2apic_mode )
+    if ( !has_assisted_xapic(v->domain) &&
+         !has_assisted_x2apic(v->domain) )
         return;
 
     vmx_vmcs_enter(v);
@@ -3395,7 +3390,7 @@ void vmx_vlapic_msr_changed(struct vcpu *v)
     if ( !vlapic_hw_disabled(vlapic) &&
          (vlapic_base_address(vlapic) == APIC_DEFAULT_PHYS_BASE) )
     {
-        if ( virtualize_x2apic_mode && vlapic_x2apic_mode(vlapic) )
+        if ( has_assisted_x2apic(v->domain) && vlapic_x2apic_mode(vlapic) )
         {
             v->arch.hvm.vmx.secondary_exec_control |=
                 SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
@@ -3416,7 +3411,7 @@ void vmx_vlapic_msr_changed(struct vcpu *v)
                 vmx_clear_msr_intercept(v, MSR_X2APIC_SELF, VMX_MSR_W);
             }
         }
-        else
+        else if ( has_assisted_xapic(v->domain) )
             v->arch.hvm.vmx.secondary_exec_control |=
                 SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
     }

xen/arch/x86/include/asm/hvm/domain.h

@@ -117,6 +117,12 @@ struct hvm_domain {
 
     bool                   is_s3_suspended;
 
+    /* xAPIC hardware assisted virtualization. */
+    bool                   assisted_xapic;
+
+    /* x2APIC hardware assisted virtualization. */
+    bool                   assisted_x2apic;
+
     /* hypervisor intercepted msix table */
     struct list_head       msixtbl_list;
 

xen/arch/x86/include/asm/hvm/hvm.h

@@ -391,6 +391,9 @@ int hvm_get_param(struct domain *d, uint32_t index, uint64_t *value);
 extern bool assisted_xapic_available;
 extern bool assisted_x2apic_available;
 
+#define has_assisted_xapic(d) ((d)->arch.hvm.assisted_xapic)
+#define has_assisted_x2apic(d) ((d)->arch.hvm.assisted_x2apic)
+
 #define hvm_get_guest_time(v) hvm_get_guest_time_fixed(v, 0)
 
 #define hvm_paging_enabled(v) \
@@ -907,6 +910,8 @@ static inline void hvm_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
 #define assisted_xapic_available false
 #define assisted_x2apic_available false
 
+#define has_assisted_xapic(d) ((void)(d), false)
+#define has_assisted_x2apic(d) ((void)(d), false)
 #define hvm_paging_enabled(v) ((void)(v), false)
 #define hvm_wp_enabled(v) ((void)(v), false)
 #define hvm_pcid_enabled(v) ((void)(v), false)

xen/arch/x86/traps.c

@@ -1117,7 +1117,8 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
         if ( !is_hvm_domain(d) || subleaf != 0 )
             break;
 
-        if ( cpu_has_vmx_apic_reg_virt )
+        if ( cpu_has_vmx_apic_reg_virt &&
+             has_assisted_xapic(d) )
             res->a |= XEN_HVM_CPUID_APIC_ACCESS_VIRT;
 
         /*
@@ -1126,7 +1127,7 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
          * and wrmsr in the guest will run without VMEXITs (see
          * vmx_vlapic_msr_changed()).
          */
-        if ( cpu_has_vmx_virtualize_x2apic_mode &&
+        if ( has_assisted_x2apic(d) &&
              cpu_has_vmx_apic_reg_virt &&
              cpu_has_vmx_virtual_intr_delivery )
             res->a |= XEN_HVM_CPUID_X2APIC_VIRT;

xen/include/public/arch-x86/xen.h

@@ -317,9 +317,14 @@ struct xen_arch_domainconfig {
  * doesn't allow the guest to read or write to the underlying MSR.
  */
 #define XEN_X86_MSR_RELAXED (1u << 0)
+#define XEN_X86_ASSISTED_XAPIC (1u << 1)
+#define XEN_X86_ASSISTED_X2APIC (1u << 2)
     uint32_t misc_flags;
 };
 
+/* Max  XEN_X86_* constant. Used for ABI checking. */
+#define XEN_X86_MISC_FLAGS_MAX XEN_X86_ASSISTED_X2APIC
+
 /* Location of online VCPU bitmap. */
 #define XEN_ACPI_CPU_MAP             0xaf00
 #define XEN_ACPI_CPU_MAP_LEN         ((HVM_MAX_VCPUS + 7) / 8)