diff --git a/sys/x86/xen/hvm.c b/sys/x86/xen/hvm.c
--- a/sys/x86/xen/hvm.c
+++ b/sys/x86/xen/hvm.c
@@ -47,6 +47,7 @@
 #include <machine/cpu.h>
 #include <machine/md_var.h>
 #include <machine/metadata.h>
+#include <machine/pc/bios.h>
 #include <machine/smp.h>
 
 #include <x86/apicreg.h>
@@ -548,3 +549,52 @@
 
 	return (regs[0] & XEN_HVM_CPUID_IOMMU_MAPPINGS);
 }
+
+int
+xen_arch_init_physmem(device_t dev, struct rman *mem)
+{
+	static struct bios_smap smap[128];
+	struct xen_memory_map memmap = {
+		.nr_entries = nitems(smap),
+	};
+	unsigned int i;
+	int error;
+
+	set_xen_guest_handle(memmap.buffer, smap);
+	error = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
+	if (error != 0)
+		return (error);
+
+	/*
+	 * Fill with UNUSABLE regions, as it's always fine to use those for
+	 * foreign mappings, they will never be populated.
+	 */
+	for (i = 0; i < memmap.nr_entries; i++) {
+		const vm_paddr_t max_phys = cpu_getmaxphyaddr();
+		vm_paddr_t start, end;
+
+		if (smap[i].type != SMAP_TYPE_ACPI_ERROR)
+			continue;
+
+		start = round_page(smap[i].base);
+		/* In 32bit mode we possibly need to truncate the addresses. */
+		end = MIN(trunc_page(smap[i].base + smap[i].length) - 1,
+		    max_phys);
+
+		if (start >= end)
+			continue;
+
+		if (bootverbose != 0)
+			device_printf(dev,
+			    "scratch mapping region @ [%016jx, %016jx]\n",
+			    start, end);
+
+		error = rman_manage_region(mem, start, end);
+		if (error != 0)
+			device_printf(dev,
+			    "unable to add scratch region [%016jx, %016jx]: %d\n",
+			    start, end, error);
+	}
+
+	return (0);
+}