diff --git a/iommu_ref_model/libiommu/include/iommu_atc.h b/iommu_ref_model/libiommu/include/iommu_atc.h
index 2cd952e8..c27c7a68 100644
--- a/iommu_ref_model/libiommu/include/iommu_atc.h
+++ b/iommu_ref_model/libiommu/include/iommu_atc.h
@@ -31,6 +31,8 @@ typedef struct {
     uint8_t  S;
     uint32_t lru;
     uint8_t  valid;
+    // Whether is an MSI translation
+    uint8_t  IS_MSI;
 } tlb_t;
 // Device directory cache
 typedef struct {
@@ -62,7 +64,7 @@ extern tlb_t       tlb[TLB_SIZE];
 extern void
 cache_ioatc_iotlb(
     uint64_t vpn, uint8_t  GV, uint8_t  PSCV, uint32_t GSCID, uint32_t PSCID,
-    pte_t *vs_pte, gpte_t *g_pte, uint64_t PPN, uint8_t S);
+    pte_t *vs_pte, gpte_t *g_pte, uint64_t PPN, uint8_t S, uint8_t is_msi);
 
 extern uint8_t
 lookup_ioatc_iotlb(
@@ -70,7 +72,7 @@ lookup_ioatc_iotlb(
     uint8_t priv, uint8_t is_read, uint8_t is_write, uint8_t is_exec,
     uint8_t SUM, uint8_t PSCV, uint32_t PSCID, uint8_t GV, uint16_t GSCID,
     uint32_t *cause, uint64_t *resp_pa, uint64_t *page_sz,
-    pte_t *vs_pte, gpte_t *g_pte);
+    pte_t *vs_pte, gpte_t *g_pteu, uint8_t *is_msi);
 
 extern uint8_t
 lookup_ioatc_dc(uint32_t device_id, device_context_t *DC);
diff --git a/iommu_ref_model/libiommu/src/iommu_atc.c b/iommu_ref_model/libiommu/src/iommu_atc.c
index d8b0319e..f9d7cd7f 100644
--- a/iommu_ref_model/libiommu/src/iommu_atc.c
+++ b/iommu_ref_model/libiommu/src/iommu_atc.c
@@ -96,7 +96,7 @@ lookup_ioatc_pc(
 void
 cache_ioatc_iotlb(
     uint64_t vpn, uint8_t  GV, uint8_t  PSCV, uint32_t GSCID, uint32_t PSCID,
-    pte_t *vs_pte, gpte_t *g_pte, uint64_t PPN, uint8_t S) {
+    pte_t *vs_pte, gpte_t *g_pte, uint64_t PPN, uint8_t S, uint8_t IS_MSI) {
 
     uint8_t i, replace = 0;
     uint32_t lru = 0xFFFFFFFF;
@@ -137,6 +137,9 @@ cache_ioatc_iotlb(
     // PPN and size
     tlb[replace].PPN   = PPN;
     tlb[replace].S     = S;
+    // Whether MSI
+    tlb[replace].IS_MSI = IS_MSI;
+
     tlb[replace].valid = 1;
     return;
 }
@@ -148,7 +151,7 @@ lookup_ioatc_iotlb(
     uint8_t priv, uint8_t is_read, uint8_t is_write, uint8_t is_exec,
     uint8_t SUM, uint8_t PSCV, uint32_t PSCID, uint8_t GV, uint16_t GSCID,
     uint32_t *cause, uint64_t *resp_pa, uint64_t *page_sz,
-    pte_t *vs_pte, gpte_t *g_pte) {
+    pte_t *vs_pte, gpte_t *g_pte, uint8_t *is_msi) {
 
     uint8_t i, hit;
     uint64_t vpn = iova / PAGESIZE;
@@ -211,6 +214,8 @@ lookup_ioatc_iotlb(
     vs_pte->G = tlb[hit].G;
     vs_pte->U = tlb[hit].U;
     vs_pte->PBMT = tlb[hit].PBMT;
+
+    *is_msi = tlb[hit].IS_MSI;
     return IOATC_HIT;
 
 page_fault:
diff --git a/iommu_ref_model/libiommu/src/iommu_translate.c b/iommu_ref_model/libiommu/src/iommu_translate.c
index 76240a6e..a2a1539d 100644
--- a/iommu_ref_model/libiommu/src/iommu_translate.c
+++ b/iommu_ref_model/libiommu/src/iommu_translate.c
@@ -276,7 +276,7 @@ iommu_translate_iova(
     check_access_perms = ( TTYP != PCIE_ATS_TRANSLATION_REQUEST ) ? 1 : 0;
     if ( (ioatc_status = lookup_ioatc_iotlb(req->tr.iova, check_access_perms, priv, is_read, is_write,
                   is_exec, SUM, PSCV, PSCID, GV, GSCID, &cause, &pa, &page_sz,
-                  &vs_pte, &g_pte)) == IOATC_FAULT )
+                  &vs_pte, &g_pte, &is_msi)) == IOATC_FAULT )
         goto stop_and_report_fault;
 
     // Hit in IOATC - complete translation.
@@ -332,15 +332,26 @@ iommu_translate_iova(
 
     // Cache the translation in the IOATC
     // In the IOTLB the IOVA & PPN is stored in the NAPOT format
+    // While IOMMUs are expected typically to cache MSI PTEs that are configured
+    // in basic translate mode (M = 3), they might not cache PTEs configured in
+    // MRIF mode (M = 1). Two reasons together justify not caching MSI PTEs in
+    // MRIF mode: First, the information and actions required to store an MSI to
+    // an MRIF are far different than normal address translation; and second, by
+    // their nature, MSIs to MRIFs should occur less frequently. Hence, an IOMMU might
+    // perform MRIF-mode processing solely as an extension of cache-miss page table
+    // walks, leaving its address translation cache oblivious to MRIF-mode MSI PTEs.
     napot_ppn = (((pa & ~(page_sz - 1)) | ((page_sz/2) - 1))/PAGESIZE);
     napot_iova = (((req->tr.iova & ~(page_sz - 1)) | ((page_sz/2) - 1))/PAGESIZE);
     napot_gpa = (((gpa & ~(page_sz - 1)) | ((page_sz/2) - 1))/PAGESIZE);
-    if ( req->tr.at == ADDR_TYPE_UNTRANSLATED ) {
+    if ( req->tr.at == ADDR_TYPE_UNTRANSLATED &&
+         (is_msi == 0 || (is_msi == 1 && is_mrif == 0)) ) {
         // For Untranslated Requests cache the translations for future re-use
         cache_ioatc_iotlb(napot_iova, GV, PSCV, iohgatp.GSCID, PSCID,
-                          &vs_pte, &g_pte, napot_ppn, ((page_sz > PAGESIZE) ? 1 : 0));
+                          &vs_pte, &g_pte, napot_ppn,
+                          ((page_sz > PAGESIZE) ? 1 : 0), is_msi);
     }
     if ( (TTYP == PCIE_ATS_TRANSLATION_REQUEST) &&
+         (is_msi == 0 || (is_msi == 1 && is_mrif == 0)) &&
          ((DC.tc.T2GPA == 1 && ((g_fill_ats_trans_in_ioatc & FILL_IOATC_ATS_T2GPA) != 0) ) ||
           ((g_fill_ats_trans_in_ioatc & FILL_IOATC_ATS_ALWAYS) != 0)) ) {
         // If in T2GPA mode, cache the final GPA->SPA translation as
@@ -350,7 +361,7 @@ iommu_translate_iova(
         cache_ioatc_iotlb((DC.tc.T2GPA == 1) ? napot_gpa : napot_iova,
                                      GV, (DC.tc.T2GPA == 1) ? 0 : PSCV,
                           iohgatp.GSCID, (DC.tc.T2GPA == 1) ? 0 : PSCID,
-                          &vs_pte, &g_pte, napot_ppn, ((page_sz > PAGESIZE) ? 1 : 0));
+                          &vs_pte, &g_pte, napot_ppn, ((page_sz > PAGESIZE) ? 1 : 0), is_msi);
         // Return the GPA as translation response if T2GPA is 1
         pa = (DC.tc.T2GPA == 1) ? gpa : pa;
     }