diff -r dc3138d60b40 xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c	Fri Jul 09 14:26:47 2010 +0100
+++ b/xen/arch/x86/hvm/hvm.c	Fri Jul 09 16:05:35 2010 +0100
@@ -3197,6 +3197,23 @@
         break;
     }
 
+    case HVMOP_xentrace: {
+        xen_hvm_xentrace_t tr;
+
+        if ( copy_from_guest(&tr, arg, 1 ) )
+            return -EFAULT;
+
+        if ( tr.extra_bytes > sizeof(tr.extra)
+             || (tr.event & ~((1u<<TRC_SUBCLS_SHIFT)-1)) )
+            return -EINVAL;
+
+        /* Cycles will be taken at the vmexit and vmenter */
+        trace_var(tr.event | TRC_GUEST, 0 /*!cycles*/,
+                  tr.extra_bytes,
+                  (unsigned char *)tr.extra);
+        break;
+    }
+
     default:
     {
         gdprintk(XENLOG_WARNING, "Bad HVM op %ld.\n", op);
diff -r dc3138d60b40 xen/include/public/hvm/hvm_op.h
--- a/xen/include/public/hvm/hvm_op.h	Fri Jul 09 14:26:47 2010 +0100
+++ b/xen/include/public/hvm/hvm_op.h	Fri Jul 09 16:05:35 2010 +0100
@@ -22,6 +22,7 @@
 #define __XEN_PUBLIC_HVM_HVM_OP_H__
 
 #include "../xen.h"
+#include "../trace.h"
 
 /* Get/set subcommands: extra argument == pointer to xen_hvm_param struct. */
 #define HVMOP_set_param           0
@@ -146,6 +147,14 @@
 typedef struct xen_hvm_get_time xen_hvm_get_time_t;
 DEFINE_XEN_GUEST_HANDLE(xen_hvm_get_time_t);
 
+#define HVMOP_xentrace              11
+struct xen_hvm_xentrace {
+    uint16_t event, extra_bytes;
+    uint8_t extra[TRACE_EXTRA_MAX * sizeof(uint32_t)];
+};
+typedef struct xen_hvm_xentrace xen_hvm_xentrace_t;
+DEFINE_XEN_GUEST_HANDLE(xen_hvm_xentrace_t);
+
 #endif /* defined(__XEN__) || defined(__XEN_TOOLS__) */
 
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
diff -r dc3138d60b40 xen/include/public/trace.h
--- a/xen/include/public/trace.h	Fri Jul 09 14:26:47 2010 +0100
+++ b/xen/include/public/trace.h	Fri Jul 09 16:05:35 2010 +0100
@@ -39,6 +39,7 @@
 #define TRC_PV       0x0020f000    /* Xen PV traces            */
 #define TRC_SHADOW   0x0040f000    /* Xen shadow tracing       */
 #define TRC_PM       0x0080f000    /* Xen power management trace */
+#define TRC_GUEST    0x0800f000    /* Guest-generated traces   */
 #define TRC_ALL      0x0ffff000
 #define TRC_HD_TO_EVENT(x) ((x)&0x0fffffff)
 #define TRC_HD_CYCLE_FLAG (1UL<<31)