diff --git a/usr.sbin/bhyve/pci_passthru.h b/usr.sbin/bhyve/pci_passthru.h
--- a/usr.sbin/bhyve/pci_passthru.h
+++ b/usr.sbin/bhyve/pci_passthru.h
@@ -11,5 +11,14 @@
 
 #include "pci_emul.h"
 
+struct passthru_softc;
+
+typedef int (*cfgread_handler)(struct passthru_softc *sc,
+    struct pci_devinst *pi, int coff, int bytes, uint32_t *rv);
+typedef int (*cfgwrite_handler)(struct passthru_softc *sc,
+    struct pci_devinst *pi, int coff, int bytes, uint32_t val);
+
 uint32_t read_config(const struct pcisel *sel, long reg, int width);
 void write_config(const struct pcisel *sel, long reg, int width, uint32_t data);
+int set_pcir_handler(struct passthru_softc *sc, int reg, int len,
+    cfgread_handler rhandler, cfgwrite_handler whandler);
diff --git a/usr.sbin/bhyve/pci_passthru.c b/usr.sbin/bhyve/pci_passthru.c
--- a/usr.sbin/bhyve/pci_passthru.c
+++ b/usr.sbin/bhyve/pci_passthru.c
@@ -93,6 +93,9 @@
 		int		capoff;
 	} psc_msix;
 	struct pcisel psc_sel;
+
+	cfgread_handler psc_pcir_rhandler[PCI_REGMAX + 1];
+	cfgwrite_handler psc_pcir_whandler[PCI_REGMAX + 1];
 };
 
 static int
@@ -643,6 +646,23 @@
 	return (error);
 }
 
+int
+set_pcir_handler(struct passthru_softc *sc, int reg, int len,
+    cfgread_handler rhandler, cfgwrite_handler whandler)
+{
+	if (reg > PCI_REGMAX || reg + len > PCI_REGMAX + 1)
+		return (-1);
+
+	for (int i = reg; i < reg + len; ++i) {
+		assert(sc->psc_pcir_rhandler[i] == NULL || rhandler == NULL);
+		assert(sc->psc_pcir_whandler[i] == NULL || whandler == NULL);
+		sc->psc_pcir_rhandler[i] = rhandler;
+		sc->psc_pcir_whandler[i] = whandler;
+	}
+
+	return (0);
+}
+
 static int
 passthru_legacy_config(nvlist_t *nvl, const char *opts)
 {
@@ -902,12 +922,9 @@
 }
 
 static int
-passthru_cfgread(struct pci_devinst *pi, int coff, int bytes, uint32_t *rv)
+passthru_cfgread_default(struct passthru_softc *sc,
+    struct pci_devinst *pi __unused, int coff, int bytes, uint32_t *rv)
 {
-	struct passthru_softc *sc;
-
-	sc = pi->pi_arg;
-
 	/*
 	 * PCI BARs and MSI capability is emulated.
 	 */
@@ -946,14 +963,25 @@
 }
 
 static int
-passthru_cfgwrite(struct pci_devinst *pi, int coff, int bytes, uint32_t val)
+passthru_cfgread(struct pci_devinst *pi, int coff, int bytes, uint32_t *rv)
 {
-	int error, msix_table_entries, i;
 	struct passthru_softc *sc;
-	uint16_t cmd_old;
 
 	sc = pi->pi_arg;
 
+	if (sc->psc_pcir_rhandler[coff] != NULL)
+		return (sc->psc_pcir_rhandler[coff](sc, pi, coff, bytes, rv));
+
+	return (passthru_cfgread_default(sc, pi, coff, bytes, rv));
+}
+
+static int
+passthru_cfgwrite_default(struct passthru_softc *sc, struct pci_devinst *pi,
+    int coff, int bytes, uint32_t val)
+{
+	int error, msix_table_entries, i;
+	uint16_t cmd_old;
+
 	/*
 	 * PCI BARs are emulated
 	 */
@@ -1026,6 +1054,19 @@
 	return (0);
 }
 
+static int
+passthru_cfgwrite(struct pci_devinst *pi, int coff, int bytes, uint32_t val)
+{
+	struct passthru_softc *sc;
+
+	sc = pi->pi_arg;
+
+	if (sc->psc_pcir_whandler[coff] != NULL)
+		return (sc->psc_pcir_whandler[coff](sc, pi, coff, bytes, val));
+
+	return (passthru_cfgwrite_default(sc, pi, coff, bytes, val));
+}
+
 static void
 passthru_write(struct pci_devinst *pi, int baridx, uint64_t offset, int size,
     uint64_t value)