[Xen-devel] [PATCH] AMD/IOMMU: correct handling when XT's prereq features are unavailable

[Jan Beulich <jbeulich@xxxxxxxx>]

We should neither cause IOMMU initialization as a whole to fail in this
case (we should still be able to bring up the system in non-x2APIC or
x2APIC physical mode), nor should the remainder of the function be
skipped (as the main part of it won't get entered a 2nd time) in such an
event. It is merely necessary for the function to indicate to the caller
(iov_supports_xt()) that setup failed as far as x2APIC is concerned.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -1364,6 +1364,7 @@ static int __init amd_iommu_prepare_one(
 int __init amd_iommu_prepare(bool xt)
 {
     struct amd_iommu *iommu;
+    bool no_xt = false;
     int rc = -ENODEV;
 
     BUG_ON( !iommu_found() );
@@ -1400,9 +1401,8 @@ int __init amd_iommu_prepare(bool xt)
         if ( rc )
             goto error_out;
 
-        rc = -ENODEV;
-        if ( xt && (!iommu->features.flds.ga_sup || 
!iommu->features.flds.xt_sup) )
-            goto error_out;
+        if ( !iommu->features.flds.ga_sup || !iommu->features.flds.xt_sup )
+            no_xt = true;
     }
 
     for_each_amd_iommu ( iommu )
@@ -1422,7 +1422,7 @@ int __init amd_iommu_prepare(bool xt)
         ivhd_type = 0;
     }
 
-    return rc;
+    return rc ?: xt && no_xt ? -ENODEV : 0;
 }
 
 int __init amd_iommu_init(bool xt)

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