x86/iommu: setup MMCFG ahead of IOMMU

Otherwise the PCI accesses to segments different than the first one done by
the IOMMU initialization code would silently fail by returning all ones.

Introduce a new helper, called pci_setup(), and move both the creation of
PCI segment 0 internal data structures, plus the parsing of ACPI MMCFG
table to it.  This moves acpi_mmcfg_init() slightly earlier from
acpi_boot_init() into pci_setup().

Note that further work will be needed to support systems where access
methods to segments different than 0 is not discoverable by Xen.

Fixes: 3950f2485b ('x86/x2APIC: defer probe until after IOMMU ACPI table parsing')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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();

xen/arch/x86/include/asm/pci.h

@@ -74,4 +74,6 @@ bool pci_check_bar(const struct pci_dev *pdev, mfn_t start, mfn_t end);
 struct rangeset;
 int pci_sanitize_bar_memory(struct rangeset *r);
 
+void pci_setup(void);
+
 #endif /* __X86_PCI_H__ */

xen/arch/x86/pci.c

@@ -6,7 +6,10 @@
 
 #include <xen/spinlock.h>
 #include <xen/pci.h>
+
+#include <asm/acpi.h>
 #include <asm/io.h>
+
 #include <xsm/xsm.h>
 
 static DEFINE_SPINLOCK(pci_config_lock);
@@ -139,6 +142,19 @@ int pci_sanitize_bar_memory(struct rangeset *r)
     return 0;
 }
 
+void __init pci_setup(void)
+{
+    /*
+     * Ahead of any ACPI table parsing make sure we have control structures
+     * for PCI segment 0.
+     */
+    if ( pci_add_segment(0) )
+        panic("Could not initialize PCI segment 0\n");
+
+    /* Parse ACPI MMCFG to see if other segments are available. */
+    acpi_mmcfg_init();
+}
+
 /*
  * Local variables:
  * mode: C

xen/arch/x86/setup.c

@@ -1938,11 +1938,10 @@ void asmlinkage __init noreturn __start_xen(void)
     setup_system_domains();
 
     /*
-     * Ahead of any ACPI table parsing make sure we have control structures
-     * for PCI segment 0.
+     * Initialize PCI (create segment 0, setup MMCFG access) ahead of IOMMU
+     * setup, as devices in segment > 0 must also be discoverable.
      */
-    if ( pci_add_segment(0) )
-        panic("Could not initialize PCI segment 0\n");
+    pci_setup();
 
     /*
      * IOMMU-related ACPI table parsing has to happen before APIC probing, for

xen/arch/x86/x86_64/mmconfig-shared.c

@@ -402,6 +402,9 @@ void __init acpi_mmcfg_init(void)
 {
     bool valid = true;
 
+    if ( acpi_disabled )
+        return;
+
     /* MMCONFIG disabled */
     if ((pci_probe & PCI_PROBE_MMCONF) == 0)
         return;