diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 48edb67..2679ef6 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -388,17 +388,18 @@ static int flush_context_reg(
     return 0;
 }
 
-static int iommu_flush_context_global(
-    struct iommu *iommu, int flush_non_present_entry)
+static int __must_check iommu_flush_context_global(struct iommu *iommu,
+                                                   int flush_non_present_entry)
 {
     struct iommu_flush *flush = iommu_get_flush(iommu);
     return flush->context(iommu, 0, 0, 0, DMA_CCMD_GLOBAL_INVL,
                                  flush_non_present_entry);
 }
 
-static int iommu_flush_context_device(
-    struct iommu *iommu, u16 did, u16 source_id,
-    u8 function_mask, int flush_non_present_entry)
+static int __must_check iommu_flush_context_device(struct iommu *iommu,
+                                                   u16 did, u16 source_id,
+                                                   u8 function_mask,
+                                                   int flush_non_present_entry)
 {
     struct iommu_flush *flush = iommu_get_flush(iommu);
     return flush->context(iommu, did, source_id, function_mask,
@@ -473,8 +474,9 @@ static int flush_iotlb_reg(void *_iommu, u16 did,
     return 0;
 }
 
-static int iommu_flush_iotlb_global(struct iommu *iommu,
-    int flush_non_present_entry, int flush_dev_iotlb)
+static int __must_check iommu_flush_iotlb_global(struct iommu *iommu,
+                                                 int flush_non_present_entry,
+                                                 int flush_dev_iotlb)
 {
     struct iommu_flush *flush = iommu_get_flush(iommu);
     int status;
@@ -491,8 +493,9 @@ static int iommu_flush_iotlb_global(struct iommu *iommu,
     return status;
 }
 
-static int iommu_flush_iotlb_dsi(struct iommu *iommu, u16 did,
-    int flush_non_present_entry, int flush_dev_iotlb)
+static int __must_check iommu_flush_iotlb_dsi(struct iommu *iommu, u16 did,
+                                              int flush_non_present_entry,
+                                              int flush_dev_iotlb)
 {
     struct iommu_flush *flush = iommu_get_flush(iommu);
     int status;
@@ -509,9 +512,10 @@ static int iommu_flush_iotlb_dsi(struct iommu *iommu, u16 did,
     return status;
 }
 
-static int iommu_flush_iotlb_psi(
-    struct iommu *iommu, u16 did, u64 addr, unsigned int order,
-    int flush_non_present_entry, int flush_dev_iotlb)
+static int __must_check iommu_flush_iotlb_psi(struct iommu *iommu, u16 did,
+                                              u64 addr, unsigned int order,
+                                              int flush_non_present_entry,
+                                              int flush_dev_iotlb)
 {
     struct iommu_flush *flush = iommu_get_flush(iommu);
     int status;
@@ -546,17 +550,37 @@ static int __must_check iommu_flush_all(void)
     struct acpi_drhd_unit *drhd;
     struct iommu *iommu;
     int flush_dev_iotlb;
+    int rc = 0;
 
     flush_all_cache();
     for_each_drhd_unit ( drhd )
     {
+        int context_rc, iotlb_rc;
+
         iommu = drhd->iommu;
-        iommu_flush_context_global(iommu, 0);
+        context_rc = iommu_flush_context_global(iommu, 0);
         flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
-        iommu_flush_iotlb_global(iommu, 0, flush_dev_iotlb);
+        iotlb_rc = iommu_flush_iotlb_global(iommu, 0, flush_dev_iotlb);
+
+        /*
+         * The current logic for returns:
+         *   - positive  invoke iommu_flush_write_buffer to flush cache.
+         *   - zero      on success.
+         *   - negative  on failure. Continue to flush IOMMU IOTLB on a
+         *               best effort basis.
+         */
+        if ( context_rc > 0 || iotlb_rc > 0 )
+            iommu_flush_write_buffer(iommu);
+        if ( context_rc >= 0 )
+            rc = context_rc;
+        if ( rc >= 0 )
+            rc = iotlb_rc;
     }
 
-    return 0;
+    if ( rc > 0 )
+        rc = 0;
+
+    return rc;
 }
 
 static int __must_check iommu_flush_iotlb(struct domain *d,
@@ -569,6 +593,7 @@ static int __must_check iommu_flush_iotlb(struct domain *d,
     struct iommu *iommu;
     int flush_dev_iotlb;
     int iommu_domid;
+    int rc = 0;
 
     /*
      * No need pcideves_lock here because we have flush
@@ -587,21 +612,23 @@ static int __must_check iommu_flush_iotlb(struct domain *d,
             continue;
 
         if ( page_count != 1 || gfn == INVALID_GFN )
-        {
-            if ( iommu_flush_iotlb_dsi(iommu, iommu_domid,
-                        0, flush_dev_iotlb) )
-                iommu_flush_write_buffer(iommu);
-        }
+            rc = iommu_flush_iotlb_dsi(iommu, iommu_domid,
+                                       0, flush_dev_iotlb);
         else
+            rc = iommu_flush_iotlb_psi(iommu, iommu_domid,
+                                       (paddr_t)gfn << PAGE_SHIFT_4K,
+                                       PAGE_ORDER_4K,
+                                       !dma_old_pte_present,
+                                       flush_dev_iotlb);
+
+        if ( rc > 0 )
         {
-            if ( iommu_flush_iotlb_psi(iommu, iommu_domid,
-                        (paddr_t)gfn << PAGE_SHIFT_4K, PAGE_ORDER_4K,
-                        !dma_old_pte_present, flush_dev_iotlb) )
-                iommu_flush_write_buffer(iommu);
+            iommu_flush_write_buffer(iommu);
+            rc = 0;
         }
     }
 
-    return 0;
+    return rc;
 }
 
 static int __must_check iommu_flush_iotlb_pages(struct domain *d,
@@ -1290,7 +1317,8 @@ int domain_context_mapping_one(
     struct context_entry *context, *context_entries;
     u64 maddr, pgd_maddr;
     u16 seg = iommu->intel->drhd->segment;
-    int agaw;
+    int agaw, rc, ret;
+    int flush_dev_iotlb;
 
     ASSERT(pcidevs_locked());
     spin_lock(&iommu->lock);
@@ -1404,14 +1432,24 @@ int domain_context_mapping_one(
     spin_unlock(&iommu->lock);
 
     /* Context entry was previously non-present (with domid 0). */
-    if ( iommu_flush_context_device(iommu, 0, (((u16)bus) << 8) | devfn,
-                                    DMA_CCMD_MASK_NOBIT, 1) )
+    rc = iommu_flush_context_device(iommu, 0, PCI_BDF2(bus, devfn),
+                                    DMA_CCMD_MASK_NOBIT, 1);
+    flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
+    ret = iommu_flush_iotlb_dsi(iommu, 0, 1, flush_dev_iotlb);
+
+    /*
+     * The current logic for returns:
+     *   - positive  invoke iommu_flush_write_buffer to flush cache.
+     *   - zero      on success.
+     *   - negative  on failure. Continue to flush IOMMU IOTLB on a
+     *               best effort basis.
+     */
+    if ( rc > 0 || ret > 0 )
         iommu_flush_write_buffer(iommu);
-    else
-    {
-        int flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
-        iommu_flush_iotlb_dsi(iommu, 0, 1, flush_dev_iotlb);
-    }
+    if ( rc >= 0 )
+        rc = ret;
+    if ( rc > 0 )
+        rc = 0;
 
     set_bit(iommu->index, &hd->arch.iommu_bitmap);
 
@@ -1420,7 +1458,7 @@ int domain_context_mapping_one(
     if ( !seg )
         me_wifi_quirk(domain, bus, devfn, MAP_ME_PHANTOM_FUNC);
 
-    return 0;
+    return rc;
 }
 
 static int domain_context_mapping(
@@ -1514,7 +1552,8 @@ int domain_context_unmap_one(
 {
     struct context_entry *context, *context_entries;
     u64 maddr;
-    int iommu_domid;
+    int iommu_domid, rc, ret;
+    int flush_dev_iotlb;
 
     ASSERT(pcidevs_locked());
     spin_lock(&iommu->lock);
@@ -1542,15 +1581,26 @@ int domain_context_unmap_one(
         return -EINVAL;
     }
 
-    if ( iommu_flush_context_device(iommu, iommu_domid,
-                                    (((u16)bus) << 8) | devfn,
-                                    DMA_CCMD_MASK_NOBIT, 0) )
+    rc = iommu_flush_context_device(iommu, iommu_domid,
+                                    PCI_BDF2(bus, devfn),
+                                    DMA_CCMD_MASK_NOBIT, 0);
+
+    flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
+    ret = iommu_flush_iotlb_dsi(iommu, iommu_domid, 0, flush_dev_iotlb);
+
+    /*
+     * The current logic for returns:
+     *   - positive  invoke iommu_flush_write_buffer to flush cache.
+     *   - zero      on success.
+     *   - negative  on failure. Continue to flush IOMMU IOTLB on a
+     *               best effort basis.
+     */
+    if ( rc > 0 || ret > 0 )
         iommu_flush_write_buffer(iommu);
-    else
-    {
-        int flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
-        iommu_flush_iotlb_dsi(iommu, iommu_domid, 0, flush_dev_iotlb);
-    }
+    if ( rc >= 0 )
+        rc = ret;
+    if ( rc > 0 )
+        rc = 0;
 
     spin_unlock(&iommu->lock);
     unmap_vtd_domain_page(context_entries);
@@ -1558,7 +1608,7 @@ int domain_context_unmap_one(
     if ( !iommu->intel->drhd->segment )
         me_wifi_quirk(domain, bus, devfn, UNMAP_ME_PHANTOM_FUNC);
 
-    return 0;
+    return rc;
 }
 
 static int domain_context_unmap(
@@ -1772,6 +1822,7 @@ int iommu_pte_flush(struct domain *d, u64 gfn, u64 *pte,
     struct domain_iommu *hd = dom_iommu(d);
     int flush_dev_iotlb;
     int iommu_domid;
+    int rc = 0;
 
     iommu_flush_cache_entry(pte, sizeof(struct dma_pte));
 
@@ -1785,13 +1836,18 @@ int iommu_pte_flush(struct domain *d, u64 gfn, u64 *pte,
         iommu_domid= domain_iommu_domid(d, iommu);
         if ( iommu_domid == -1 )
             continue;
-        if ( iommu_flush_iotlb_psi(iommu, iommu_domid,
+
+        rc = iommu_flush_iotlb_psi(iommu, iommu_domid,
                                    (paddr_t)gfn << PAGE_SHIFT_4K,
-                                   order, !present, flush_dev_iotlb) )
+                                   order, !present, flush_dev_iotlb);
+        if ( rc > 0 )
+        {
             iommu_flush_write_buffer(iommu);
+            rc = 0;
+        }
     }
 
-    return 0;
+    return rc;
 }
 
 static int __init vtd_ept_page_compatible(struct iommu *iommu)
