x86/APIC: avoid iommu_supports_x2apic() on error path

The value it returns may change from true to false in case
iommu_enable_x2apic() fails and, as a side effect, clears iommu_intremap
(as can happen at least on AMD). Latch the return value from the first
invocation to replace the second one.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 0f50d1696b3c13cbf0b18fec817fc291d5a30a31
master date: 2021-11-04 14:44:43 +0100

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index 4a2740ccea056c0f9543e96cf4e38515efc93c00..789af8c4da7e57b12be04a455983bccdbe8cf980 100644 (file)
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -864,6 +864,7 @@ void x2apic_ap_setup(void)
 void __init x2apic_bsp_setup(void)
 {
     struct IO_APIC_route_entry **ioapic_entries = NULL;
+    bool iommu_x2apic;
     const char *orig_name;
 
     if ( !cpu_has_x2apic )
@@ -879,7 +880,8 @@ void __init x2apic_bsp_setup(void)
         printk("x2APIC: Already enabled by BIOS: Ignoring cmdline disable.\n");
     }
 
-    if ( iommu_supports_x2apic() )
+    iommu_x2apic = iommu_supports_x2apic();
+    if ( iommu_x2apic )
     {
         if ( (ioapic_entries = alloc_ioapic_entries()) == NULL )
         {
@@ -932,8 +934,11 @@ void __init x2apic_bsp_setup(void)
         printk("Switched to APIC driver %s\n", genapic.name);
 
 restore_out:
-    /* iommu_x2apic_enabled cannot be used here in the error case. */
-    if ( iommu_supports_x2apic() )
+    /*
+     * iommu_x2apic_enabled and iommu_supports_x2apic() cannot be used here
+     * in the error case.
+     */
+    if ( iommu_x2apic )
     {
         /*
          * NB: do not use raw mode when restoring entries if the iommu has