Index: sys/amd64/amd64/pmap.c
===================================================================
--- sys/amd64/amd64/pmap.c
+++ sys/amd64/amd64/pmap.c
@@ -1331,6 +1331,8 @@
 	return (pg_nx);
 }
 
+static int kern_promoted_end;
+
 static void
 create_pagetables(vm_paddr_t *firstaddr)
 {
@@ -1396,10 +1398,12 @@
 	KPTphys = allocpages(firstaddr, nkpt);
 	KPDphys = allocpages(firstaddr, nkpdpe);
 
-	/* Fill in the underlying page table pages */
-	/* XXX not fully used, underneath 2M pages */
+	/*
+	 * Fill in the underlying page table pages.  Only used when
+	 * PTmap mappings are demoted.
+	 */
 	pt_p = (pt_entry_t *)KPTphys;
-	for (i = 0; ptoa(i) < *firstaddr; i++)
+	for (i = 0; ptoa(i) < round_2mpage(*firstaddr); i++)
 		pt_p[i] = ptoa(i) | X86_PG_V | pg_g | bootaddr_rwx(ptoa(i));
 
 	/* Now map the page tables at their location within PTmap */
@@ -1407,13 +1411,16 @@
 	for (i = 0; i < nkpt; i++)
 		pd_p[i] = (KPTphys + ptoa(i)) | X86_PG_RW | X86_PG_V;
 
-	/* Map from zero to end of allocations under 2M pages */
-	/* This replaces some of the KPTphys entries above */
-	for (i = 0; (i << PDRSHIFT) < *firstaddr; i++)
+	/*
+	 * Map from zero to end of allocations under 2M pages.
+	 * This replaces some of the KPTphys entries above.
+	 */
+	kern_promoted_end = *firstaddr;
+	for (i = 0; (i << PDRSHIFT) < kern_promoted_end; i++)
 		/* Preset PG_M and PG_A because demotion expects it. */
 		pd_p[i] = (i << PDRSHIFT) | X86_PG_V | PG_PS | pg_g |
 		    X86_PG_M | X86_PG_A | bootaddr_rwx(i << PDRSHIFT);
-
+	kern_promoted_end = i;
 	/*
 	 * Because we map the physical blocks in 2M pages, adjust firstaddr
 	 * to record the physical blocks we've actually mapped into kernel
@@ -1750,7 +1757,7 @@
 		mpte->pindex = pmap_pde_pindex(KERNBASE) + i;
 		mpte->phys_addr = KPTphys + (i << PAGE_SHIFT);
 		mpte->wire_count = 1;
-		if (i << PDRSHIFT < KERNend &&
+		if (i < kern_promoted_end &&
 		    pmap_insert_pt_page(kernel_pmap, mpte))
 			panic("pmap_init: pmap_insert_pt_page failed");
 	}
@@ -4480,6 +4487,51 @@
 	return (rv);
 }
 
+static void
+pmap_demote_pde_check(pt_entry_t *firstpte __unused, pt_entry_t newpte __unused)
+{
+#ifdef INVARIANTS
+#ifdef DIAGNOSTIC
+	pt_entry_t *xpte, *ypte;
+
+	for (xpte = firstpte; xpte < firstpte + NPTEPG; xpte++) {
+		if ((*xpte & PG_FRAME) != (newpte & PG_FRAME) +
+		    ptoa(xpte - firstpte)) {
+			printf("pmap_demote_pde: xpte %zd and newpte map "
+			    "different pages %#lx %#lx\n",
+			    xpte - firstpte, *xpte, newpte);
+			printf("XX %lx %lx\n", (*xpte & PG_FRAME),
+			    (newpte & PG_FRAME) + ptoa(xpte - firstpte));
+			for (ypte = firstpte; ypte < firstpte + NPTEPG; ypte++)
+				printf("%zd %#lx\n", ypte - firstpte, *ypte);
+			panic("firstpte");
+		}
+	}
+#else
+	KASSERT((*firstpte & PG_FRAME) == (newpte & PG_FRAME),
+	    ("pmap_demote_pde: firstpte and newpte map different physical"
+	    " addresses"));
+#endif
+#endif
+}
+
+static void
+pmap_demote_pde_fail(pmap_t pmap, vm_offset_t va, pd_entry_t *pde,
+    pd_entry_t oldpde, struct rwlock **lockp)
+{
+	struct spglist free;
+	vm_offset_t sva;
+
+	SLIST_INIT(&free);
+	sva = trunc_2mpage(va);
+	pmap_remove_pde(pmap, pde, sva, &free, lockp);
+	if ((oldpde & pmap_global_bit(pmap)) == 0)
+		pmap_invalidate_pde_page(pmap, sva, oldpde);
+	vm_page_free_pages_toq(&free, true);
+	CTR2(KTR_PMAP, "pmap_demote_pde: failure for va %#lx"
+	    " in pmap %p", va, pmap);
+}
+
 static boolean_t
 pmap_demote_pde_locked(pmap_t pmap, pd_entry_t *pde, vm_offset_t va,
     struct rwlock **lockp)
@@ -4489,12 +4541,11 @@
 	pt_entry_t PG_A, PG_G, PG_M, PG_PKU_MASK, PG_RW, PG_V;
 	vm_paddr_t mptepa;
 	vm_page_t mpte;
-	struct spglist free;
-	vm_offset_t sva;
 	int PG_PTE_CACHE;
+	bool in_kernel;
 
-	PG_G = pmap_global_bit(pmap);
 	PG_A = pmap_accessed_bit(pmap);
+	PG_G = pmap_global_bit(pmap);
 	PG_M = pmap_modified_bit(pmap);
 	PG_RW = pmap_rw_bit(pmap);
 	PG_V = pmap_valid_bit(pmap);
@@ -4502,14 +4553,22 @@
 	PG_PKU_MASK = pmap_pku_mask_bit(pmap);
 
 	PMAP_LOCK_ASSERT(pmap, MA_OWNED);
+	in_kernel = va >= VM_MAXUSER_ADDRESS;
 	oldpde = *pde;
 	KASSERT((oldpde & (PG_PS | PG_V)) == (PG_PS | PG_V),
 	    ("pmap_demote_pde: oldpde is missing PG_PS and/or PG_V"));
-	if ((oldpde & PG_A) == 0 || (mpte = pmap_remove_pt_page(pmap, va)) ==
-	    NULL) {
+	if ((oldpde & PG_A) == 0) {
+		pmap_demote_pde_fail(pmap, va, pde, oldpde, lockp);
+		return (FALSE);
+	}
+	mpte = pmap_remove_pt_page(pmap, va);
+	if (mpte == NULL) {
 		KASSERT((oldpde & PG_W) == 0,
 		    ("pmap_demote_pde: page table page for a wired mapping"
 		    " is missing"));
+		KASSERT(!in_kernel || (va >= DMAP_MIN_ADDRESS &&
+		    va < DMAP_MAX_ADDRESS),
+		    ("pmap_demote_pde: No saved mpte for va %#lx", va));
 
 		/*
 		 * Invalidate the 2MB page mapping and return "failure" if the
@@ -4523,22 +4582,17 @@
 		 * is the only part of the kernel address space that must be
 		 * handled here.
 		 */
-		if ((oldpde & PG_A) == 0 || (mpte = vm_page_alloc(NULL,
-		    pmap_pde_pindex(va), (va >= DMAP_MIN_ADDRESS && va <
-		    DMAP_MAX_ADDRESS ? VM_ALLOC_INTERRUPT : VM_ALLOC_NORMAL) |
-		    VM_ALLOC_NOOBJ | VM_ALLOC_WIRED)) == NULL) {
-			SLIST_INIT(&free);
-			sva = trunc_2mpage(va);
-			pmap_remove_pde(pmap, pde, sva, &free, lockp);
-			if ((oldpde & PG_G) == 0)
-				pmap_invalidate_pde_page(pmap, sva, oldpde);
-			vm_page_free_pages_toq(&free, true);
-			CTR2(KTR_PMAP, "pmap_demote_pde: failure for va %#lx"
-			    " in pmap %p", va, pmap);
+		mpte = vm_page_alloc(NULL, pmap_pde_pindex(va),
+		    (in_kernel ? VM_ALLOC_INTERRUPT : VM_ALLOC_NORMAL) |
+		    VM_ALLOC_NOOBJ | VM_ALLOC_WIRED);
+		if (mpte == NULL) {
+			pmap_demote_pde_fail(pmap, va, pde, oldpde, lockp);
 			return (FALSE);
 		}
-		if (va < VM_MAXUSER_ADDRESS)
+		if (!in_kernel) {
+			mpte->wire_count = NPTEPG;
 			pmap_resident_count_inc(pmap, 1);
+		}
 	}
 	mptepa = VM_PAGE_TO_PHYS(mpte);
 	firstpte = (pt_entry_t *)PHYS_TO_DMAP(mptepa);
@@ -4553,13 +4607,9 @@
 	/*
 	 * If the page table page is new, initialize it.
 	 */
-	if (mpte->wire_count == 1) {
-		mpte->wire_count = NPTEPG;
+	if ((oldpde & PG_PROMOTED) == 0)
 		pmap_fill_ptp(firstpte, newpte);
-	}
-	KASSERT((*firstpte & PG_FRAME) == (newpte & PG_FRAME),
-	    ("pmap_demote_pde: firstpte and newpte map different physical"
-	    " addresses"));
+	pmap_demote_pde_check(firstpte, newpte);
 
 	/*
 	 * If the mapping has changed attributes, update the page table
@@ -4594,7 +4644,7 @@
 	/*
 	 * Invalidate a stale recursive mapping of the page table page.
 	 */
-	if (va >= VM_MAXUSER_ADDRESS)
+	if (in_kernel)
 		pmap_invalidate_page(pmap, (vm_offset_t)vtopte(va));
 
 	/*