[xen staging] x86/iommu: setup MMCFG ahead of IOMMU

[patchbot@xxxxxxx]

commit c292772b4945d3a264a61c3c1920f1aebd17998b
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Aug 18 10:16:36 2025 +0200
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Thu Aug 21 11:57:25 2025 +0200

    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: 3950f2485bbc ('x86/x2APIC: defer probe until after IOMMU ACPI table 
parsing')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/acpi/boot.c              |  2 --
 xen/arch/x86/include/asm/pci.h        |  2 ++
 xen/arch/x86/pci.c                    | 16 ++++++++++++++++
 xen/arch/x86/setup.c                  |  7 +++----
 xen/arch/x86/x86_64/mmconfig-shared.c |  3 +++
 5 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/acpi/boot.c b/xen/arch/x86/acpi/boot.c
index 3901f9d982..1ca2360e00 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/include/asm/pci.h b/xen/arch/x86/include/asm/pci.h
index 665b321165..0b98081aea 100644
--- a/xen/arch/x86/include/asm/pci.h
+++ b/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__ */
diff --git a/xen/arch/x86/pci.c b/xen/arch/x86/pci.c
index 26bb7f6a3c..fd0715fb6a 100644
--- a/xen/arch/x86/pci.c
+++ b/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
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 6fb42c5a5f..52c8a7adab 100644
--- a/xen/arch/x86/setup.c
+++ b/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
diff --git a/xen/arch/x86/x86_64/mmconfig-shared.c 
b/xen/arch/x86/x86_64/mmconfig-shared.c
index f1a3d42c5b..fbe2676f86 100644
--- a/xen/arch/x86/x86_64/mmconfig-shared.c
+++ b/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;
--
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