Index: head/sys/amd64/amd64/pmap.c
===================================================================
--- head/sys/amd64/amd64/pmap.c
+++ head/sys/amd64/amd64/pmap.c
@@ -1290,7 +1290,35 @@
 	struct pmap_preinit_mapping *ppim;
 	vm_page_t mpte;
 	vm_size_t s;
-	int error, i, pv_npg;
+	int error, i, pv_npg, ret, skz63;
+
+	/* Detect bare-metal Skylake Server and Skylake-X. */
+	if (vm_guest == VM_GUEST_NO && cpu_vendor_id == CPU_VENDOR_INTEL &&
+	    CPUID_TO_FAMILY(cpu_id) == 0x6 && CPUID_TO_MODEL(cpu_id) == 0x55) {
+		/*
+		 * Skylake-X errata SKZ63. Processor May Hang When
+		 * Executing Code In an HLE Transaction Region between
+		 * 40000000H and 403FFFFFH.
+		 *
+		 * Mark the pages in the range as preallocated.  It
+		 * seems to be impossible to distinguish between
+		 * Skylake Server and Skylake X.
+		 */
+		skz63 = 1;
+		TUNABLE_INT_FETCH("hw.skz63_enable", &skz63);
+		if (skz63 != 0) {
+			if (bootverbose)
+				printf("SKZ63: skipping 4M RAM starting "
+				    "at physical 1G\n");
+			for (i = 0; i < atop(0x400000); i++) {
+				ret = vm_page_blacklist_add(0x40000000 +
+				    ptoa(i), FALSE);
+				if (!ret && bootverbose)
+					printf("page at %#lx already used\n",
+					    0x40000000 + ptoa(i));
+			}
+		}
+	}
 
 	/*
 	 * Initialize the vm page array entries for the kernel pmap's
Index: head/sys/vm/vm_page.h
===================================================================
--- head/sys/vm/vm_page.h
+++ head/sys/vm/vm_page.h
@@ -476,6 +476,7 @@
     vm_memattr_t memattr);
 vm_page_t vm_page_alloc_freelist(int, int);
 vm_page_t vm_page_alloc_freelist_domain(int, int, int);
+bool vm_page_blacklist_add(vm_paddr_t pa, bool verbose);
 void vm_page_change_lock(vm_page_t m, struct mtx **mtx);
 vm_page_t vm_page_grab (vm_object_t, vm_pindex_t, int);
 int vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
Index: head/sys/vm/vm_page.c
===================================================================
--- head/sys/vm/vm_page.c
+++ head/sys/vm/vm_page.c
@@ -341,6 +341,29 @@
 	return (0);
 }
 
+bool
+vm_page_blacklist_add(vm_paddr_t pa, bool verbose)
+{
+	struct vm_domain *vmd;
+	vm_page_t m;
+	int ret;
+
+	m = vm_phys_paddr_to_vm_page(pa);
+	if (m == NULL)
+		return (true); /* page does not exist, no failure */
+
+	vmd = vm_pagequeue_domain(m);
+	vm_domain_free_lock(vmd);
+	ret = vm_phys_unfree_page(m);
+	vm_domain_free_unlock(vmd);
+	if (ret) {
+		TAILQ_INSERT_TAIL(&blacklist_head, m, listq);
+		if (verbose)
+			printf("Skipping page with pa 0x%jx\n", (uintmax_t)pa);
+	}
+	return (ret);
+}
+
 /*
  *	vm_page_blacklist_check:
  *
@@ -351,29 +374,14 @@
 static void
 vm_page_blacklist_check(char *list, char *end)
 {
-	struct vm_domain *vmd;
 	vm_paddr_t pa;
-	vm_page_t m;
 	char *next;
-	int ret;
 
 	next = list;
 	while (next != NULL) {
 		if ((pa = vm_page_blacklist_next(&next, end)) == 0)
 			continue;
-		m = vm_phys_paddr_to_vm_page(pa);
-		if (m == NULL)
-			continue;
-		vmd = vm_pagequeue_domain(m);
-		vm_domain_free_lock(vmd);
-		ret = vm_phys_unfree_page(m);
-		vm_domain_free_unlock(vmd);
-		if (ret == TRUE) {
-			TAILQ_INSERT_TAIL(&blacklist_head, m, listq);
-			if (bootverbose)
-				printf("Skipping page with pa 0x%jx\n",
-				    (uintmax_t)pa);
-		}
+		vm_page_blacklist_add(pa, bootverbose);
 	}
 }