Index: sys/amd64/include/vmparam.h
===================================================================
--- sys/amd64/include/vmparam.h
+++ sys/amd64/include/vmparam.h
@@ -233,6 +233,8 @@
 #define	VM_MAX_ADDRESS		UPT_MAX_ADDRESS
 #define	VM_MIN_ADDRESS		(0)
 
+#define	VM_MAX_PHYS_ADDRESS	(cpu_getmaxphyaddr())
+
 /*
  * XXX Allowing dmaplimit == 0 is a temporary workaround for vt(4) efifb's
  * early use of PHYS_TO_DMAP before the mapping is actually setup. This works
Index: sys/arm/include/vmparam.h
===================================================================
--- sys/arm/include/vmparam.h
+++ sys/arm/include/vmparam.h
@@ -139,6 +139,8 @@
 #endif
 #define VM_MAX_ADDRESS          VM_MAXUSER_ADDRESS
 
+#define	VM_MAX_PHYS_ADDRESS	0xFFFFFFFFull
+
 #define	SHAREDPAGE		(VM_MAXUSER_ADDRESS - PAGE_SIZE)
 #define	USRSTACK		SHAREDPAGE
 
Index: sys/arm64/include/vmparam.h
===================================================================
--- sys/arm64/include/vmparam.h
+++ sys/arm64/include/vmparam.h
@@ -152,6 +152,8 @@
 #define	VM_MIN_ADDRESS		(0x0000000000000000UL)
 #define	VM_MAX_ADDRESS		(0xffffffffffffffffUL)
 
+#define	VM_MAX_PHYS_ADDRESS	VM_MAX_ADDRESS
+
 /* 512 GiB of kernel addresses */
 #define	VM_MIN_KERNEL_ADDRESS	(0xffff000000000000UL)
 #define	VM_MAX_KERNEL_ADDRESS	(0xffff008000000000UL)
Index: sys/i386/include/vmparam.h
===================================================================
--- sys/i386/include/vmparam.h
+++ sys/i386/include/vmparam.h
@@ -172,6 +172,8 @@
 #define VM_MAX_ADDRESS		VADDR(PTDPTDI, 0)
 #define VM_MIN_ADDRESS		((vm_offset_t)0)
 
+#define	VM_MAX_PHYS_ADDRESS	(cpu_getmaxphyaddr())
+
 #define	PMAP_TRM_MIN_ADDRESS	VM_MAXUSER_ADDRESS
 #define	PMAP_TRM_MAX_ADDRESS	0xffffffff
 
Index: sys/kern/subr_physmem.c
===================================================================
--- sys/kern/subr_physmem.c
+++ sys/kern/subr_physmem.c
@@ -40,6 +40,7 @@
 #include <sys/systm.h>
 #include <sys/kernel.h>
 #include <sys/physmem.h>
+#include <machine/md_var.h>
 #include <vm/vm.h>
 #include <vm/vm_param.h>
 #include <vm/vm_page.h>
@@ -62,15 +63,9 @@
 #define	MAX_EXCNT	16
 #endif
 
-#if defined(__arm__)
-#define	MAX_PHYS_ADDR	0xFFFFFFFFull
-#elif defined(__aarch64__) || defined(__riscv)
-#define	MAX_PHYS_ADDR	0xFFFFFFFFFFFFFFFFull
-#endif
-
 struct region {
 	vm_paddr_t	addr;
-	vm_size_t	size;
+	vm_ooffset_t	size;
 	uint32_t	flags;
 };
 
@@ -166,8 +161,9 @@
 	availsz = 0;
 	acnt = 0;
 	for (hwi = 0, hwp = hwregions; hwi < hwcnt; ++hwi, ++hwp) {
-		start = hwp->addr;
-		end   = hwp->size + start;
+		/* Operate on page boundaries.  Partial pages aren't usable. */
+		start = round_page(hwp->addr);
+		end   = trunc_page(hwp->size + start);
 		totalmem += atop((vm_offset_t)(end - start));
 		for (exi = 0, exp = exregions; exi < excnt; ++exi, ++exp) {
 			/*
@@ -176,8 +172,9 @@
 			 */
 			if ((exp->flags & exflags) == 0)
 				continue;
-			xstart = exp->addr;
-			xend   = exp->size + xstart;
+			/* Whole page is excluded. */
+			xstart = trunc_page(exp->addr);
+			xend = round_page(exp->size + xstart);
 			/*
 			 * If the excluded region ends before this hw region,
 			 * continue checking with the next excluded region.
@@ -336,7 +333,7 @@
  */
 static size_t
 insert_region(struct region *regions, size_t rcnt, vm_paddr_t addr,
-    vm_size_t size, uint32_t flags)
+    vm_ooffset_t size, uint32_t flags)
 {
 	size_t i;
 	vm_paddr_t nend, rend;
@@ -393,7 +390,6 @@
 int
 physmem_hardware_region(uint64_t pa, uint64_t sz)
 {
-	vm_offset_t adj;
 
 	/*
 	 * Filter out the page at PA 0x00000000.  The VM can't handle it, as
@@ -404,7 +400,7 @@
 			return (0);
 		pa = PAGE_SIZE;
 		sz -= PAGE_SIZE;
-	} else if (pa > MAX_PHYS_ADDR) {
+	} else if (pa > VM_MAX_PHYS_ADDRESS) {
 		/* This range is past usable memory, ignore it */
 		return (ERANGE);
 	}
@@ -420,21 +416,13 @@
 	 * pointer deref in _vm_map_lock_read().  Better to give up a megabyte
 	 * than leave some folks with an unusable system while we investigate.
 	 */
-	if ((pa + sz) > (MAX_PHYS_ADDR - 1024 * 1024)) {
-		sz = MAX_PHYS_ADDR - pa + 1;
+	if ((pa + sz) > (VM_MAX_PHYS_ADDRESS - 1024 * 1024)) {
+		sz = VM_MAX_PHYS_ADDRESS - pa + 1;
 		if (sz <= 1024 * 1024)
 			return (0);
 		sz -= 1024 * 1024;
 	}
 
-	/*
-	 * Round the starting address up to a page boundary, and truncate the
-	 * ending page down to a page boundary.
-	 */
-	adj = round_page(pa) - pa;
-	pa  = round_page(pa);
-	sz  = trunc_page(sz - adj);
-
 	if (sz == 0)
 		return (EINVAL);
 	if (hwcnt == nitems(hwregions))
@@ -447,17 +435,8 @@
  * Add an exclusion region.
  */
 int
-physmem_exclude_region(vm_paddr_t pa, vm_size_t sz, uint32_t exflags)
+physmem_exclude_region(uint64_t pa, uint64_t sz, uint32_t exflags)
 {
-	vm_offset_t adj;
-
-	/*
-	 * Truncate the starting address down to a page boundary, and round the
-	 * ending page up to a page boundary.
-	 */
-	adj = pa - trunc_page(pa);
-	pa  = trunc_page(pa);
-	sz  = round_page(sz + adj);
 
 	if (excnt == nitems(exregions))
 		return (E2BIG);
Index: sys/mips/include/vmparam.h
===================================================================
--- sys/mips/include/vmparam.h
+++ sys/mips/include/vmparam.h
@@ -79,6 +79,8 @@
 #define	VM_MIN_ADDRESS		((vm_offset_t)0x00000000)
 #define	VM_MAX_ADDRESS		((vm_offset_t)(intptr_t)(int32_t)0xffffffff)
 
+#define	VM_MAX_PHYS_ADDRESS	VM_MAX_ADDRESS
+
 #define	VM_MINUSER_ADDRESS	((vm_offset_t)0x00000000)
 
 #ifdef __mips_n64
Index: sys/powerpc/include/vmparam.h
===================================================================
--- sys/powerpc/include/vmparam.h
+++ sys/powerpc/include/vmparam.h
@@ -104,6 +104,7 @@
 #define	VM_MAXUSER_ADDRESS	VM_MAXUSER_ADDRESS32
 #define	VM_MAX_ADDRESS		0xffffffff
 #endif
+#define	VM_MAX_PHYS_ADDRESS	VM_MAX_ADDRESS
 
 #define	SHAREDPAGE		(VM_MAXUSER_ADDRESS - PAGE_SIZE)
 
Index: sys/riscv/include/vmparam.h
===================================================================
--- sys/riscv/include/vmparam.h
+++ sys/riscv/include/vmparam.h
@@ -147,6 +147,8 @@
 #define	VM_MIN_ADDRESS		(0x0000000000000000UL)
 #define	VM_MAX_ADDRESS		(0xffffffffffffffffUL)
 
+#define	VM_MAX_PHYS_ADDRESS	VM_MAX_ADDRESS
+
 #define	VM_MIN_KERNEL_ADDRESS	(0xffffffc000000000UL)
 #define	VM_MAX_KERNEL_ADDRESS	(0xffffffc800000000UL)
 
Index: sys/sys/physmem.h
===================================================================
--- sys/sys/physmem.h
+++ sys/sys/physmem.h
@@ -50,7 +50,7 @@
 #define	EXFLAG_NOALLOC	0x02
 
 int physmem_hardware_region(uint64_t pa, uint64_t sz);
-int physmem_exclude_region(vm_paddr_t pa, vm_size_t sz, uint32_t flags);
+int physmem_exclude_region(uint64_t pa, uint64_t sz, uint32_t flags);
 size_t physmem_avail(vm_paddr_t *avail, size_t maxavail);
 void physmem_init_kernel_globals(size_t *pa_idx, size_t *da_idx);
 void physmem_print_tables(void);