diff -r eccfdeb41b80 tools/libxc/xc_cpuid_x86.c
--- a/tools/libxc/xc_cpuid_x86.c	Tue Aug 24 18:42:59 2010 +0100
+++ b/tools/libxc/xc_cpuid_x86.c	Wed Aug 25 13:34:54 2010 +0200
@@ -117,9 +117,8 @@
     case 0x80000008:
         /*
          * ECX[15:12] is ApicIdCoreSize: ECX[7:0] is NumberOfCores (minus one).
-         * Update to reflect vLAPIC_ID = vCPU_ID * 2.
          */
-        regs[2] = ((regs[2] & 0xf000u) + 1) | ((regs[2] & 0xffu) << 1) | 1u;
+        regs[2] &= 0xf0ffu;
         break;
     }
 }
@@ -134,11 +133,9 @@
     case 0x00000004:
         /*
          * EAX[31:26] is Maximum Cores Per Package (minus one).
-         * Update to reflect vLAPIC_ID = vCPU_ID * 2.
          */
-        regs[0] = (((regs[0] & 0x7c000000u) << 1) | 0x04000000u |
-                   (regs[0] & 0x3ffu));
-        regs[3] &= 0x3ffu;
+        regs[0] &= 0xfc0003ffu;
+        regs[3] &= 0x00000003u;
         break;
 
     case 0x80000001: {
@@ -185,9 +182,8 @@
     case 0x00000001:
         /*
          * EBX[23:16] is Maximum Logical Processors Per Package.
-         * Update to reflect vLAPIC_ID = vCPU_ID * 2.
          */
-        regs[1] = (regs[1] & 0x0000ffffu) | ((regs[1] & 0x007f0000u) << 1);
+        regs[1] & 0x00ffffffu;
 
         regs[2] &= (bitmaskof(X86_FEATURE_XMM3) |
                     bitmaskof(X86_FEATURE_SSSE3) |