Index: xen-3.4.1-testing/xen/arch/x86/hvm/hyperv/hv_intercept.c
===================================================================
--- xen-3.4.1-testing.orig/xen/arch/x86/hvm/hyperv/hv_intercept.c	2009-08-10 14:01:45.000000000 -0600
+++ xen-3.4.1-testing/xen/arch/x86/hvm/hyperv/hv_intercept.c	2009-08-10 14:07:15.000000000 -0600
@@ -33,6 +33,7 @@
 
 #include <asm/config.h>
 #include <asm/hvm/io.h>
+#include <asm/hvm/support.h>
 #include <asm/processor.h>
 #include <asm/page.h>
 #include <asm/apicdef.h>
@@ -987,8 +988,15 @@
         break;
     case HV_MSR_APIC_ASSIST_PAGE:
         /*
-         * For now ignore this.
+         * We don't support the APIC assist page; windows7 appears to
+         * use this; set it up so that os uses the APIC MSR to indicate EOI.
          */
+        if (msr_content & 0x1) {
+	    uint32_t data = 0;
+	    paddr_t assist_page = msr_content & ~1UL;
+	    (void)hvm_copy_to_guest_phys(assist_page, &data, sizeof(data));
+	}	
+
         break;
 
     default: