Index: /trunk/src/VBox/VMM/VMMR3/CPUMR3CpuId.cpp
===================================================================
--- /trunk/src/VBox/VMM/VMMR3/CPUMR3CpuId.cpp	(revision 54919)
+++ /trunk/src/VBox/VMM/VMMR3/CPUMR3CpuId.cpp	(revision 54920)
@@ -2045,4 +2045,5 @@
     CPUMISAEXTCFG   enmMisAlnSse;
     CPUMISAEXTCFG   enm3dNowPrf;
+    CPUMISAEXTCFG   enmAmdExtMmx;
 
     uint32_t        uMaxStdLeaf;
@@ -2500,5 +2501,5 @@
                                //| X86_CPUID_EXT_FEATURE_EDX_NX     - enabled later by PGM
                                //| RT_BIT_32(21)                    - reserved
-                               //| X86_CPUID_AMD_FEATURE_EDX_AXMMX
+                               | (pConfig->enmAmdExtMmx ? X86_CPUID_AMD_FEATURE_EDX_AXMMX : 0)
                                | X86_CPUID_AMD_FEATURE_EDX_MMX
                                | X86_CPUID_AMD_FEATURE_EDX_FXSR
@@ -2561,4 +2562,5 @@
             PORTABLE_DISABLE_FEATURE_BIT(    1, pExtFeatureLeaf->uEcx, TBM,        X86_CPUID_AMD_FEATURE_ECX_TBM);
             PORTABLE_DISABLE_FEATURE_BIT(    1, pExtFeatureLeaf->uEcx, FMA4,       X86_CPUID_AMD_FEATURE_ECX_FMA4);
+            PORTABLE_DISABLE_FEATURE_BIT_CFG(1, pExtFeatureLeaf->uEdx, AXMMX,      X86_CPUID_AMD_FEATURE_EDX_AXMMX,     pConfig->enmAmdExtMmx);
             PORTABLE_DISABLE_FEATURE_BIT(    1, pExtFeatureLeaf->uEdx, 3DNOW,      X86_CPUID_AMD_FEATURE_EDX_3DNOW);
             PORTABLE_DISABLE_FEATURE_BIT(    1, pExtFeatureLeaf->uEdx, 3DNOW_EX,   X86_CPUID_AMD_FEATURE_EDX_3DNOW_EX);
@@ -2599,4 +2601,6 @@
         if (pConfig->enm3dNowPrf  == CPUMISAEXTCFG_ENABLED_ALWAYS)
             pExtFeatureLeaf->uEcx |= X86_CPUID_AMD_FEATURE_ECX_3DNOWPRF;
+        if (pConfig->enmAmdExtMmx  == CPUMISAEXTCFG_ENABLED_ALWAYS)
+            pExtFeatureLeaf->uEdx |= X86_CPUID_AMD_FEATURE_EDX_AXMMX;
     }
     pExtFeatureLeaf = NULL; /* Must refetch! */
@@ -3568,4 +3572,12 @@
      */
     rc = cpumR3CpuIdReadIsaExtCfg(pVM, pIsaExts, "3DNOWPRF", &pConfig->enm3dNowPrf, fNestedPagingAndFullGuestExec);
+    AssertLogRelRCReturn(rc, rc);
+
+    /** @cfgm{/CPUM/IsaExts/AXMMX, isaextcfg, depends}
+     * Whether to expose the AMD's MMX Extensions to the guest.  For the time being
+     * the default is to only do this for VMs with nested paging and AMD-V or
+     * unrestricted guest mode.
+     */
+    rc = cpumR3CpuIdReadIsaExtCfg(pVM, pIsaExts, "AXMMX", &pConfig->enmAmdExtMmx, fNestedPagingAndFullGuestExec);
     AssertLogRelRCReturn(rc, rc);