Index: /trunk/src/VBox/VMM/CPUM.cpp
===================================================================
--- /trunk/src/VBox/VMM/CPUM.cpp	(revision 26650)
+++ /trunk/src/VBox/VMM/CPUM.cpp	(revision 26651)
@@ -817,4 +817,12 @@
         pVCpu->cpum.s.pHyperCoreRC = MMHyperCCToRC(pVM, pVCpu->cpum.s.pHyperCoreR3);
         Assert(pVCpu->cpum.s.pHyperCoreRC != NIL_RTRCPTR);
+
+        /*
+         * Workaround for missing cpuid(0) patches when leaf 4 returns GuestCpuIdDef:
+         * If we miss to patch a cpuid(0).eax then Linux tries to determine the number
+         * of processors from (cpuid(4).eax >> 26) + 1.
+         */
+        if (!HWACCMR3IsAllowed(pVM))
+            pCPUM->aGuestCpuIdStd[4].eax = 0;
     }
 }