diff --git a/xen/arch/x86/acpi/boot.c b/xen/arch/x86/acpi/boot.c
index 170f9783c5..aa9ab1a2e3 100644
--- a/xen/arch/x86/acpi/boot.c
+++ b/xen/arch/x86/acpi/boot.c
@@ -748,8 +748,6 @@ int __init acpi_boot_init(void)
 
 	acpi_table_parse(ACPI_SIG_HPET, acpi_parse_hpet);
 
-	acpi_mmcfg_init();
-
 	erst_init();
 
 	acpi_hest_init();
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 2148dde05f..a123f94e85 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1802,6 +1802,12 @@ void asmlinkage __init noreturn __start_xen(unsigned long mbi_p)
      */
     setup_system_domains();
 
+    /*
+     * Initialize PCI (create segment 0, setup MMCFG access) ahead of IOMMU
+     * setup, as devices in segment > 0 must also be discoverable.
+     */
+    acpi_mmcfg_init();
+
     /*
      * IOMMU-related ACPI table parsing has to happen before APIC probing, for
      * check_x2apic_preenabled() to be able to observe respective findings, in
diff --git a/xen/arch/x86/x86_64/mmconfig-shared.c b/xen/arch/x86/x86_64/mmconfig-shared.c
index b3b2da7362..7818ae5c3f 100644
--- a/xen/arch/x86/x86_64/mmconfig-shared.c
+++ b/xen/arch/x86/x86_64/mmconfig-shared.c
@@ -403,6 +403,9 @@ void __init acpi_mmcfg_init(void)
 
     pci_segments_init();
 
+    if ( acpi_disabled )
+        return;
+
     /* MMCONFIG disabled */
     if ((pci_probe & PCI_PROBE_MMCONF) == 0)
         return;