[xen staging] VT-d: don't lose errors when flushing TLBs on multiple IOMMUs

[patchbot@xxxxxxx]

commit e7059776f9755b989a992d229c68c3d7778412be
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 24 16:30:06 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 24 16:30:06 2021 +0200

    VT-d: don't lose errors when flushing TLBs on multiple IOMMUs
    
    While no longer an immediate problem with flushes no longer timing out,
    errors (if any) get properly reported by iommu_flush_iotlb_{dsi,psi}().
    Overwriting such an error with, perhaps, a success indicator received
    from another IOMMU will misguide callers. Record the first error, but
    don't bail from the loop (such that further necessary invalidation gets
    carried out on a best effort basis).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index f3524a1def..0f10951ce9 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -643,7 +643,7 @@ static int __must_check iommu_flush_iotlb(struct domain *d, 
dfn_t dfn,
     struct vtd_iommu *iommu;
     bool_t flush_dev_iotlb;
     int iommu_domid;
-    int rc = 0;
+    int ret = 0;
 
     /*
      * No need pcideves_lock here because we have flush
@@ -651,6 +651,8 @@ static int __must_check iommu_flush_iotlb(struct domain *d, 
dfn_t dfn,
      */
     for_each_drhd_unit ( drhd )
     {
+        int rc;
+
         iommu = drhd->iommu;
 
         if ( !test_bit(iommu->index, &hd->arch.vtd.iommu_bitmap) )
@@ -673,13 +675,12 @@ static int __must_check iommu_flush_iotlb(struct domain 
*d, dfn_t dfn,
                                        flush_dev_iotlb);
 
         if ( rc > 0 )
-        {
             iommu_flush_write_buffer(iommu);
-            rc = 0;
-        }
+        else if ( !ret )
+            ret = rc;
     }
 
-    return rc;
+    return ret;
 }
 
 static int __must_check iommu_flush_iotlb_pages(struct domain *d,
--
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