diff -r 985f5fa8fc59 tools/libxc/xc_cpuid_x86.c
--- a/tools/libxc/xc_cpuid_x86.c	Mon Nov 08 17:25:54 2010 +0000
+++ b/tools/libxc/xc_cpuid_x86.c	Tue Nov 09 10:41:09 2010 +0800
@@ -195,7 +195,8 @@ static void xc_cpuid_hvm_policy(
                     bitmaskof(X86_FEATURE_SSE4_1) |
                     bitmaskof(X86_FEATURE_SSE4_2) |
                     bitmaskof(X86_FEATURE_POPCNT) |
-                    bitmaskof(X86_FEATURE_AES));
+                    bitmaskof(X86_FEATURE_AES) |
+                    bitmaskof(X86_FEATURE_AVX));
 
         regs[2] |= bitmaskof(X86_FEATURE_HYPERVISOR);
 
@@ -281,6 +282,7 @@ static void xc_cpuid_pv_policy(
 {
     DECLARE_DOMCTL;
     int guest_64bit, xen_64bit = hypervisor_is_64bit(xch);
+    int xsave_supported = 0;
     char brand[13];
 
     xc_cpuid_brand_get(brand);
@@ -290,6 +292,17 @@ static void xc_cpuid_pv_policy(
     domctl.cmd = XEN_DOMCTL_get_address_size;
     do_domctl(xch, &domctl);
     guest_64bit = (domctl.u.address_size.size == 64);
+
+    /* Detecting Xen's atitude towards XSAVE */
+    memset(&domctl, 0, sizeof(domctl));
+    domctl.cmd = XEN_DOMCTL_getvcpuextstate;
+    domctl.domain = domid;
+    domctl.u.vcpuextstate.vcpu = 0;
+    domctl.u.vcpuextstate.size = 0;
+    domctl.u.vcpuextstate.xfeature_mask = 0;
+    do_domctl(xch, &domctl);
+    if ( domctl.u.vcpuextstate.xfeature_mask != 0 )
+        xsave_supported = 1;
 
     if ( (input[0] & 0x7fffffff) == 1 )
     {
@@ -320,10 +333,11 @@ static void xc_cpuid_pv_policy(
         clear_bit(X86_FEATURE_TM2, regs[2]);
         if ( !guest_64bit )
             clear_bit(X86_FEATURE_CX16, regs[2]);
+        if ( !xsave_supported )
+            clear_bit(X86_FEATURE_XSAVE, regs[2]);
         clear_bit(X86_FEATURE_XTPR, regs[2]);
         clear_bit(X86_FEATURE_PDCM, regs[2]);
         clear_bit(X86_FEATURE_DCA, regs[2]);
-        clear_bit(X86_FEATURE_XSAVE, regs[2]);
         set_bit(X86_FEATURE_HYPERVISOR, regs[2]);
         break;
     case 0x80000001:
diff -r 985f5fa8fc59 xen/arch/x86/traps.c
--- a/xen/arch/x86/traps.c	Mon Nov 08 17:25:54 2010 +0000
+++ b/xen/arch/x86/traps.c	Tue Nov 09 09:40:27 2010 +0800
@@ -795,7 +795,8 @@ static void pv_cpuid(struct cpu_user_reg
         __clear_bit(X86_FEATURE_XTPR % 32, &c);
         __clear_bit(X86_FEATURE_PDCM % 32, &c);
         __clear_bit(X86_FEATURE_DCA % 32, &c);
-        __clear_bit(X86_FEATURE_XSAVE % 32, &c);
+        if ( !cpu_has_xsave )
+			__clear_bit(X86_FEATURE_XSAVE % 32, &c);
         if ( !cpu_has_apic )
            __clear_bit(X86_FEATURE_X2APIC % 32, &c);
         __set_bit(X86_FEATURE_HYPERVISOR % 32, &c);