diff --git a/arch/i386/pci/mmconfig.c b/arch/i386/pci/mmconfig.c
index 5fbaa91..60f0e7a 100644
--- a/arch/i386/pci/mmconfig.c
+++ b/arch/i386/pci/mmconfig.c
@@ -22,10 +22,31 @@
 /*
  * Functions for accessing PCI configuration space with MMCONFIG accesses
  */
-
-static inline void pci_exp_set_dev_base(int bus, int devfn)
+static u32 get_base_addr(unsigned int seg, int bus)
 {
-	u32 dev_base = pci_mmcfg_config[0].base_address | (bus << 20) | (devfn << 12);
+	int cfg_num = -1;
+	struct acpi_table_mcfg_config *cfg;
+
+	while (1) {
+		++cfg_num;
+		if (cfg_num >= pci_mmcfg_config_num) {
+			/* something bad is going on, no cfg table is found. */
+			/* so we fall back to the old way we used to do this */
+			/* and just rely on the first entry to be correct. */
+			return pci_mmcfg_config[0].base_address;
+		}
+		cfg = &pci_mmcfg_config[cfg_num];
+		if (cfg->pci_segment_group_number != seg)
+			continue;
+		if ((cfg->start_bus_number <= bus) &&
+		    (cfg->end_bus_number >= bus))
+			return cfg->base_address;
+	}
+}
+
+static inline void pci_exp_set_dev_base(unsigned int seg, int bus, int devfn)
+{
+	u32 dev_base = get_base_addr(seg, bus) | (bus << 20) | (devfn << 12);
 	if (dev_base != mmcfg_last_accessed_device) {
 		mmcfg_last_accessed_device = dev_base;
 		set_fixmap_nocache(FIX_PCIE_MCFG, dev_base);
@@ -42,7 +63,7 @@
 
 	spin_lock_irqsave(&pci_config_lock, flags);
 
-	pci_exp_set_dev_base(bus, devfn);
+	pci_exp_set_dev_base(seg, bus, devfn);
 
 	switch (len) {
 	case 1:
@@ -71,7 +92,7 @@
 
 	spin_lock_irqsave(&pci_config_lock, flags);
 
-	pci_exp_set_dev_base(bus, devfn);
+	pci_exp_set_dev_base(seg, bus, devfn);
 
 	switch (len) {
 	case 1: