Index: sys/conf/files
===================================================================
--- sys/conf/files
+++ sys/conf/files
@@ -5136,6 +5136,7 @@
 vm/vm_swapout_dummy.c		optional NO_SWAPPING
 vm/vm_unix.c			standard
 vm/vnode_pager.c		standard
+xen/common.c			optional xenhvm
 xen/features.c			optional xenhvm
 xen/xenbus/xenbus_if.m		optional xenhvm
 xen/xenbus/xenbus.c		optional xenhvm
Index: sys/x86/xen/hvm.c
===================================================================
--- sys/x86/xen/hvm.c
+++ sys/x86/xen/hvm.c
@@ -66,8 +66,6 @@
 static void xen_hvm_cpu_init(void);
 
 /*-------------------------------- Global Data -------------------------------*/
-enum xen_domain_type xen_domain_type = XEN_NATIVE;
-
 #ifdef SMP
 struct cpu_ops xen_hvm_cpu_ops = {
 	.cpu_init	= xen_hvm_cpu_init,
@@ -83,12 +81,6 @@
  */
 int xen_vector_callback_enabled;
 
-/**
- * Start info flags. ATM this only used to store the initial domain flag for
- * PVHv2, and it's always empty for HVM guests.
- */
-uint32_t hvm_start_flags;
-
 /**
  * Signal whether the vector injected for the event channel upcall requires to
  * be EOI'ed on the local APIC.
@@ -99,9 +91,6 @@
 DPCPU_DEFINE(struct vcpu_info, vcpu_local_info);
 DPCPU_DEFINE(struct vcpu_info *, vcpu_info);
 
-/*------------------ Hypervisor Access Shared Memory Regions -----------------*/
-shared_info_t *HYPERVISOR_shared_info;
-
 /*------------------------------ Sysctl tunables -----------------------------*/
 int xen_disable_pv_disks = 0;
 int xen_disable_pv_nics = 0;
@@ -203,33 +192,6 @@
 	return (0);
 }
 
-static void
-xen_hvm_init_shared_info_page(void)
-{
-	struct xen_add_to_physmap xatp;
-
-	if (xen_pv_domain()) {
-		/*
-		 * Already setup in the PV case, shared_info is passed inside
-		 * of the start_info struct at start of day.
-		 */
-		return;
-	}
-
-	if (HYPERVISOR_shared_info == NULL) {
-		HYPERVISOR_shared_info = malloc(PAGE_SIZE, M_XENHVM, M_NOWAIT);
-		if (HYPERVISOR_shared_info == NULL)
-			panic("Unable to allocate Xen shared info page");
-	}
-
-	xatp.domid = DOMID_SELF;
-	xatp.idx = 0;
-	xatp.space = XENMAPSPACE_shared_info;
-	xatp.gpfn = vtophys(HYPERVISOR_shared_info) >> PAGE_SHIFT;
-	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
-		panic("HYPERVISOR_memory_op failed");
-}
-
 static int
 set_percpu_callback(unsigned int vcpu)
 {
@@ -397,7 +359,7 @@
 	 * is passed inside the start_info struct and is already set, so this
 	 * functions are no-ops.
 	 */
-	xen_hvm_init_shared_info_page();
+	xen_handle_shared_info(0);
 	xen_hvm_disable_emulated_devices();
 } 
 
Index: sys/xen/common.c
===================================================================
--- /dev/null
+++ sys/xen/common.c
@@ -0,0 +1,97 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2021 Elliott Mitchell
+ * Copyright (c) 2014 Julien Grall
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <sys/param.h> /* required by xen/xen-os.h */
+
+#include <sys/kernel.h>
+
+#include <vm/vm.h>
+#include <vm/vm_page.h>
+
+#include <machine/atomic.h> /* required by xen/xen-os.h */
+
+#include <xen/xen-os.h>
+#include <xen/hvm.h>
+
+#include <xen/interface/event_channel.h>
+#include <xen/interface/hvm/params.h>
+
+/*-------------------------------- Global Data -------------------------------*/
+enum xen_domain_type xen_domain_type = XEN_NATIVE;
+
+/**
+ * Start info flags. ATM this only used to store the initial domain flag for
+ * PVHv2, and it's always empty for HVM guests.
+ */
+uint32_t hvm_start_flags;
+
+/*------------------ Hypervisor Access Shared Memory Regions -----------------*/
+shared_info_t *HYPERVISOR_shared_info = NULL;
+
+void
+xen_handle_shared_info(const void *arg __unused)
+{
+	struct xen_add_to_physmap xatp;
+	vm_page_t shared_info;
+
+	if (!xen_hvm_domain()) {
+		/*
+		 * Already setup in the PV case, shared_info is passed inside
+		 * of the start_info struct at start of day.
+		 */
+		return;
+	}
+
+	/*
+	 * We expect to be called multiple times, the shared info page needs
+	 * to be re-registered on resume.
+	 */
+	if (HYPERVISOR_shared_info == NULL) {
+		shared_info = vm_page_alloc(NULL, 0, VM_ALLOC_NOOBJ | VM_ALLOC_ZERO);
+		if (shared_info == NULL)
+			panic("Unable to allocate Xen shared info page\n");
+		HYPERVISOR_shared_info = pmap_mapdev_attr(
+		    VM_PAGE_TO_PHYS(shared_info), PAGE_SIZE, VM_MEMATTR_XEN);
+
+	}
+
+	xatp.domid = DOMID_SELF;
+	xatp.idx = 0;
+	xatp.space = XENMAPSPACE_shared_info;
+	xatp.gpfn = vtophys(HYPERVISOR_shared_info) >> PAGE_SHIFT;
+	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
+		panic("Unable to map shared info\n");
+}
+
+/* reserve SI_ORDER_FIRST for probing presence of Xen */
+C_SYSINIT(xen_shared_info, SI_SUB_HYPERVISOR, SI_ORDER_SECOND, xen_handle_shared_info, NULL);
Index: sys/xen/hvm.h
===================================================================
--- sys/xen/hvm.h
+++ sys/xen/hvm.h
@@ -102,6 +102,7 @@
 void xen_hvm_set_callback(device_t);
 void xen_hvm_suspend(void);
 void xen_hvm_resume(bool suspend_cancelled);
+void xen_handle_shared_info(const void *__unused);
 
 extern uint32_t hvm_start_flags;
 extern bool xen_evtchn_needs_ack;