Index: sys/dev/pci/pci.c
===================================================================
--- sys/dev/pci/pci.c
+++ sys/dev/pci/pci.c
@@ -80,6 +80,8 @@
 #include "pcib_if.h"
 #include "pci_if.h"
 
+#define	PCI_MAX_FUNC_ALIASES	255
+
 #define	PCIR_IS_BIOS(cfg, reg)						\
 	(((cfg)->hdrtype == PCIM_HDRTYPE_NORMAL && reg == PCIR_BIOS) ||	\
 	 ((cfg)->hdrtype == PCIM_HDRTYPE_BRIDGE && reg == PCIR_BIOS_1))
@@ -502,6 +504,81 @@
 	return (retval);
 }
 
+static pcicfgregs *
+pci_dev_to_cfg(device_t dev)
+{
+	struct pci_devinfo *dinfo;
+	pcicfgregs *cfg;
+	bool found;
+
+	found = false;
+
+	STAILQ_FOREACH(dinfo, &pci_devq, pci_links) {
+		if (dinfo->cfg.dev == dev) {
+			found = true;
+			break;
+		}
+	}
+
+	if (!found)
+		return (NULL);
+
+	cfg = &dinfo->cfg;
+
+	return (cfg);
+}
+
+int
+pci_add_dma_alias(device_t dev, uint8_t devfn_from, uint8_t nr_devfns)
+{
+	pcicfgregs *cfg;
+
+	if (nr_devfns == 0)
+		return (EINVAL);
+
+	if ((devfn_from + nr_devfns - 1) > PCI_MAX_FUNC_ALIASES)
+		return (EINVAL);
+
+	cfg = pci_dev_to_cfg(dev);
+	if (cfg == NULL)
+		return (ENODEV);
+
+	mtx_lock_spin(&cfg->dma_aliases_mtx);
+	bit_nset(cfg->dma_aliases, devfn_from, nr_devfns);
+	mtx_unlock_spin(&cfg->dma_aliases_mtx);
+
+	return (0);
+}
+
+int
+pci_for_each_dma_alias(device_t dev, int (*fn)(device_t dev,
+    uint8_t alias, void *data), void *data)
+{
+	pcicfgregs *cfg;
+	int n;
+
+	cfg = pci_dev_to_cfg(dev);
+	if (cfg == NULL)
+		return (ENODEV);
+
+	if (cfg->dma_aliases == NULL)
+		return (ENOENT);
+
+	mtx_lock_spin(&cfg->dma_aliases_mtx);
+	bit_ffs_at(cfg->dma_aliases, 0, PCI_MAX_FUNC_ALIASES, &n);
+	mtx_unlock_spin(&cfg->dma_aliases_mtx);
+
+	while (n >= 0) {
+		fn(dev, n, data);
+
+		mtx_lock_spin(&cfg->dma_aliases_mtx);
+		bit_ffs_at(cfg->dma_aliases, n + 1, PCI_MAX_FUNC_ALIASES, &n);
+		mtx_unlock_spin(&cfg->dma_aliases_mtx);
+	}
+
+	return (0);
+}
+
 /* return base address of memory or port map */
 
 static pci_addr_t
@@ -705,6 +782,10 @@
 
 	cfg->iov		= NULL;
 
+	mtx_init(&cfg->dma_aliases_mtx, "alias bit set", NULL, MTX_SPIN);
+	cfg->dma_aliases = bit_alloc(PCI_MAX_FUNC_ALIASES, M_DEVBUF,
+	    M_WAITOK | M_ZERO);
+
 	pci_fixancient(cfg);
 	pci_hdrtypedata(pcib, b, s, f, cfg);
 
@@ -2717,6 +2798,8 @@
 		free(pm, M_DEVBUF);
 	}
 	STAILQ_REMOVE(devlist_head, dinfo, pci_devinfo, pci_links);
+	mtx_destroy(&dinfo->cfg.dma_aliases_mtx);
+	free(&dinfo->cfg.dma_aliases, M_DEVBUF);
 	free(dinfo, M_DEVBUF);
 
 	/* increment the generation count */
Index: sys/dev/pci/pcivar.h
===================================================================
--- sys/dev/pci/pcivar.h
+++ sys/dev/pci/pcivar.h
@@ -31,6 +31,7 @@
 #ifndef _PCIVAR_H_
 #define	_PCIVAR_H_
 
+#include <sys/bitstring.h>
 #include <sys/queue.h>
 #include <sys/_eventhandler.h>
 
@@ -212,6 +213,9 @@
 
     uint32_t	flags;		/* flags defined above */
 
+    bitstr_t	*dma_aliases;	/* PCI function aliases for IOMMU. */
+    struct mtx	dma_aliases_mtx; /* protection for aliases bitstr */
+
     struct pcicfg_bridge bridge; /* Bridges */
     struct pcicfg_pp pp;	/* Power management */
     struct pcicfg_vpd vpd;	/* Vital product data */
@@ -694,6 +698,10 @@
 
 void	pci_print_faulted_dev(void);
 
+int	pci_add_dma_alias(device_t dev, uint8_t devfn_from, uint8_t nr_devfns);
+int	pci_for_each_dma_alias(device_t dev, int (*fn)(device_t dev,
+	    uint8_t alias, void *data), void *data);
+
 #endif	/* _SYS_BUS_H_ */
 
 /*