Index: usr.sbin/bhyve/pci_emul.c
===================================================================
--- usr.sbin/bhyve/pci_emul.c
+++ usr.sbin/bhyve/pci_emul.c
@@ -46,6 +46,8 @@
 
 #include <machine/vmm.h>
 #include <machine/vmm_snapshot.h>
+#include <machine/cpufunc.h>
+#include <machine/specialreg.h>
 #include <vmmapi.h>
 
 #include "acpi.h"
@@ -98,6 +100,7 @@
 static uint64_t pci_emul_iobase;
 static uint64_t pci_emul_membase32;
 static uint64_t pci_emul_membase64;
+static uint64_t pci_emul_memresv64;
 
 #define	PCI_EMUL_IOBASE		0x2000
 #define	PCI_EMUL_IOLIMIT	0x10000
@@ -108,9 +111,6 @@
 
 #define	PCI_EMUL_MEMLIMIT32	PCI_EMUL_ECFG_BASE
 
-#define	PCI_EMUL_MEMBASE64	0xD000000000UL
-#define	PCI_EMUL_MEMLIMIT64	0xFD00000000UL
-
 static struct pci_devemu *pci_emul_finddev(char *name);
 static void pci_lintr_route(struct pci_devinst *pi);
 static void pci_lintr_update(struct pci_devinst *pi);
@@ -622,9 +622,9 @@
 		 * Some drivers do not work well if the 64-bit BAR is allocated
 		 * above 4GB. Allow for this by allocating small requests under
 		 * 4GB unless then allocation size is larger than some arbitrary
-		 * number (32MB currently).
+		 * number (128MB currently).
 		 */
-		if (size > 32 * 1024 * 1024) {
+		if (size > 128 * 1024 * 1024) {
 			/*
 			 * XXX special case for device requiring peer-peer DMA
 			 */
@@ -632,7 +632,7 @@
 				baseptr = &hostbase;
 			else
 				baseptr = &pci_emul_membase64;
-			limit = PCI_EMUL_MEMLIMIT64;
+			limit = pci_emul_memresv64;
 			mask = PCIM_BAR_MEM_BASE;
 			lobits = PCIM_BAR_MEM_SPACE | PCIM_BAR_MEM_64 |
 				 PCIM_BAR_MEM_PREFETCH;
@@ -1101,12 +1101,22 @@
 	struct slotinfo *si;
 	struct funcinfo *fi;
 	size_t lowmem;
-	int bus, slot, func;
-	int error;
+	uint64_t cpu_maxphysaddr;
+	u_int regs[4];
+	int bus, slot, func, error;
 
 	pci_emul_iobase = PCI_EMUL_IOBASE;
 	pci_emul_membase32 = vm_get_lowmem_limit(ctx);
-	pci_emul_membase64 = PCI_EMUL_MEMBASE64;
+
+	do_cpuid(0x80000008, regs);
+	cpu_maxphysaddr = 1ULL << (regs[0] & 0xff);
+	pci_emul_memresv64 = cpu_maxphysaddr / 4;
+	/*
+	 * Max power of 2 that is less then
+	 * cpu_maxphysaddr - pci_emul_memresv64.
+	 */
+	pci_emul_membase64 = 1ULL << (flsl(cpu_maxphysaddr -
+	    pci_emul_memresv64) - 1);
 
 	for (bus = 0; bus < MAXBUSES; bus++) {
 		if ((bi = pci_businfo[bus]) == NULL)