[xen staging] x86/x2APIC: defer probe until after IOMMU ACPI table parsing

[patchbot@xxxxxxx]

commit 3950f2485bbc983c5c9f66ef9637395e975a2bec
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Dec 3 11:36:10 2021 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 3 11:36:10 2021 +0100

    x86/x2APIC: defer probe until after IOMMU ACPI table parsing
    
    While commit 46c4061cd2bf ("x86/IOMMU: mark IOMMU / intremap not in use
    when ACPI tables are missing") deals with apic_x2apic_probe() as called
    from x2apic_bsp_setup(), the check_x2apic_preenabled() path is similarly
    affected: The call needs to occur after acpi_iommu_init(), such that
    iommu_intremap getting disabled there can be properly taken into account
    by apic_x2apic_probe().
    
    Note that, for the time being (further cleanup patches following),
    reversing the order of the calls to generic_apic_probe() and
    acpi_boot_init() is not an option:
    - acpi_process_madt() calls clustered_apic_check() and hence relies on
      genapic to have got filled before,
    - generic_bigsmp_probe() (called from acpi_process_madt()) needs to
      occur after generic_apic_probe(),
    - acpi_parse_madt() (called from acpi_process_madt()) calls
      acpi_madt_oem_check(), which wants to be after generic_apic_probe().
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/acpi/boot.c            |  2 --
 xen/arch/x86/setup.c                | 19 +++++++++++++++++--
 xen/drivers/passthrough/x86/iommu.c | 11 +++++++----
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/acpi/boot.c b/xen/arch/x86/acpi/boot.c
index 24702d041c..cc4bbc0284 100644
--- a/xen/arch/x86/acpi/boot.c
+++ b/xen/arch/x86/acpi/boot.c
@@ -742,8 +742,6 @@ int __init acpi_boot_init(void)
 
        acpi_mmcfg_init();
 
-       acpi_iommu_init();
-
        erst_init();
 
        acpi_hest_init();
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 723bd49c76..f40a9fe5d3 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1664,15 +1664,30 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 
     dmi_scan_machine();
 
-    generic_apic_probe();
-
     mmio_ro_ranges = rangeset_new(NULL, "r/o mmio ranges",
                                   RANGESETF_prettyprint_hex);
 
     xsm_multiboot_init(module_map, mbi);
 
+    /*
+     * IOMMU-related ACPI table parsing may require some of the system domains
+     * to be usable, e.g. for pci_hide_device()'s use of dom_xen.
+     */
     setup_system_domains();
 
+    /*
+     * IOMMU-related ACPI table parsing has to happen before APIC probing, for
+     * check_x2apic_preenabled() to be able to observe respective findings, in
+     * particular iommu_intremap having got turned off.
+     */
+    acpi_iommu_init();
+
+    /*
+     * APIC probing needs to happen before general ACPI table parsing, as e.g.
+     * generic_bigsmp_probe() may occur only afterwards.
+     */
+    generic_apic_probe();
+
     acpi_boot_init();
 
     if ( smp_found_config )
diff --git a/xen/drivers/passthrough/x86/iommu.c 
b/xen/drivers/passthrough/x86/iommu.c
index b2284ae001..f11280f4b2 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -43,14 +43,17 @@ bool __read_mostly iommu_intpost;
 
 void __init acpi_iommu_init(void)
 {
-    int ret;
+    int ret = -ENODEV;
 
     if ( !iommu_enable && !iommu_intremap )
         return;
 
-    ret = acpi_dmar_init();
-    if ( ret == -ENODEV )
-        ret = acpi_ivrs_init();
+    if ( !acpi_disabled )
+    {
+        ret = acpi_dmar_init();
+        if ( ret == -ENODEV )
+            ret = acpi_ivrs_init();
+    }
 
     if ( ret )
     {
--
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