[xen stable-4.15] x86/APIC: avoid iommu_supports_x2apic() on error path

[patchbot@xxxxxxx]

commit 2fb9c599d0ca5d1d44daa8bbf8692bcbe907ee14
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Nov 19 09:32:34 2021 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Nov 19 09:32:34 2021 +0100

    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@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    master commit: 0f50d1696b3c13cbf0b18fec817fc291d5a30a31
    master date: 2021-11-04 14:44:43 +0100
---
 xen/arch/x86/apic.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index 8ab8214559..030792cabb 100644
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -865,6 +865,7 @@ 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 )
@@ -880,7 +881,8 @@ 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 )
         {
@@ -933,8 +935,11 @@ 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
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15