diff -uNr xen-unstable.hg-handle_ro/tools/libxc/xc_misc.c xen-unstable.hg-hvmop_set_mem/tools/libxc/xc_misc.c
--- xen-unstable.hg-handle_ro/tools/libxc/xc_misc.c	2008-07-04 11:18:18.000000000 +0100
+++ xen-unstable.hg-hvmop_set_mem/tools/libxc/xc_misc.c	2008-07-10 11:24:21.911281083 +0100
@@ -295,6 +295,36 @@
     return rc;
 }
 
+int xc_hvm_set_mem_type(
+    int xc_handle, domid_t dom, hvmmem_type_t mem_type, uint64_t first_pfn, uint64_t nr)
+{
+    DECLARE_HYPERCALL;
+    struct xen_hvm_set_mem_type arg;
+    int rc;
+
+    hypercall.op     = __HYPERVISOR_hvm_op;
+    hypercall.arg[0] = HVMOP_set_mem_type;
+    hypercall.arg[1] = (unsigned long)&arg;
+
+    arg.domid        = dom;
+    arg.hvmmem_type  = mem_type;
+    arg.first_pfn    = first_pfn;
+    arg.nr           = nr;
+
+    if ( (rc = lock_pages(&arg, sizeof(arg))) != 0 )
+    {
+        PERROR("Could not lock memory");
+        return rc;
+    }
+
+    rc = do_xen_hypercall(xc_handle, &hypercall);
+
+    unlock_pages(&arg, sizeof(arg));
+
+    return rc;
+}
+
+
 void *xc_map_foreign_pages(int xc_handle, uint32_t dom, int prot,
                            const xen_pfn_t *arr, int num)
 {
diff -uNr xen-unstable.hg-handle_ro/tools/libxc/xenctrl.h xen-unstable.hg-hvmop_set_mem/tools/libxc/xenctrl.h
--- xen-unstable.hg-handle_ro/tools/libxc/xenctrl.h	2008-07-08 15:52:49.000000000 +0100
+++ xen-unstable.hg-hvmop_set_mem/tools/libxc/xenctrl.h	2008-07-10 11:24:21.915281333 +0100
@@ -27,6 +27,7 @@
 #include <xen/event_channel.h>
 #include <xen/sched.h>
 #include <xen/memory.h>
+#include <xen/hvm/params.h>
 #include <xen/xsm/acm.h>
 #include <xen/xsm/acm_ops.h>
 #include <xen/xsm/flask_op.h>
@@ -942,6 +943,14 @@
 int xc_hvm_modified_memory(
     int xc_handle, domid_t dom, uint64_t first_pfn, uint64_t nr);
 
+/*
+ * Set a range of memory to a specific type.
+ * Allowed types are HVMMEM_ram_rw, HVMMEM_ram_ro, HVMMEM_mmio_dm
+ */
+int xc_hvm_set_mem_type(
+    int xc_handle, domid_t dom, hvmmem_type_t memtype, uint64_t first_pfn, uint64_t nr);
+
+
 typedef enum {
   XC_ERROR_NONE = 0,
   XC_INTERNAL_ERROR = 1,
diff -uNr xen-unstable.hg-handle_ro/xen/arch/x86/hvm/hvm.c xen-unstable.hg-hvmop_set_mem/xen/arch/x86/hvm/hvm.c
--- xen-unstable.hg-handle_ro/xen/arch/x86/hvm/hvm.c	2008-07-10 11:18:37.449753583 +0100
+++ xen-unstable.hg-hvmop_set_mem/xen/arch/x86/hvm/hvm.c	2008-07-10 11:24:21.915281333 +0100
@@ -2613,6 +2613,65 @@
         break;
     }
 
+    case HVMOP_set_mem_type:
+    {
+        struct xen_hvm_set_mem_type a;
+        struct domain *d;
+        unsigned long pfn;
+        
+        /* Interface types to internal p2m types */
+        p2m_type_t memtype[3] = {
+            p2m_ram_rw,        /* HVMMEM_ram_rw  */
+            p2m_ram_ro,        /* HVMMEM_ram_ro  */
+            p2m_mmio_dm,       /* HVMMEM_mmio_dm */
+        };
+
+        if ( copy_from_guest(&a, arg, 1) )
+            return -EFAULT;
+
+        if ( a.domid == DOMID_SELF )
+        {
+            d = rcu_lock_current_domain();
+        }
+        else
+        {
+            if ( (d = rcu_lock_domain_by_id(a.domid)) == NULL )
+                return -ESRCH;
+            if ( !IS_PRIV_FOR(current->domain, d) )
+            {
+                rc = -EPERM;
+                goto param_fail4;
+            }
+        }
+
+        rc = -EINVAL;
+        if ( !is_hvm_domain(d) )
+            goto param_fail4;
+
+        rc = -EINVAL;
+        if ( (a.first_pfn > domain_get_maximum_gpfn(d)) ||
+             ((a.first_pfn + a.nr - 1) < a.first_pfn) ||
+             ((a.first_pfn + a.nr - 1) > domain_get_maximum_gpfn(d)) )
+            goto param_fail4;
+            
+        if ( a.hvmmem_type >= 3 )
+            goto param_fail4;
+            
+        rc = 0;
+        
+        for ( pfn = a.first_pfn; pfn < a.first_pfn + a.nr; pfn++ )
+        {
+            mfn_t mfn;
+            p2m_type_t t;
+            mfn = gfn_to_mfn(d, pfn, &t);
+            p2m_change_type(d,pfn,t, memtype[a.hvmmem_type]);
+        }
+         
+    param_fail4:
+        rcu_unlock_domain(d);
+        break;
+    }
+
     default:
     {
         gdprintk(XENLOG_WARNING, "Bad HVM op %ld.\n", op);
diff -uNr xen-unstable.hg-handle_ro/xen/include/public/hvm/hvm_op.h xen-unstable.hg-hvmop_set_mem/xen/include/public/hvm/hvm_op.h
--- xen-unstable.hg-handle_ro/xen/include/public/hvm/hvm_op.h	2008-07-04 11:18:19.000000000 +0100
+++ xen-unstable.hg-hvmop_set_mem/xen/include/public/hvm/hvm_op.h	2008-07-10 11:24:21.915281333 +0100
@@ -105,6 +105,27 @@
 typedef struct xen_hvm_modified_memory xen_hvm_modified_memory_t;
 DEFINE_XEN_GUEST_HANDLE(xen_hvm_modified_memory_t);
 
+#define HVMOP_set_mem_type    8
+typedef enum {
+    HVMMEM_ram_rw,             /* Normal read/write guest RAM */
+    HVMMEM_ram_ro,             /* Read-only; writes go to the device model */
+    HVMMEM_mmio_dm,            /* Reads and write go to the device model */
+} hvmmem_type_t;
+/* Notify that a section of ram is to be treated as ROM. */
+struct xen_hvm_set_mem_type {
+    /* Domain to be updated. */
+    domid_t  domid;
+    /* Memory type */
+    hvmmem_type_t hvmmem_type;
+    /* First pfn. */
+    uint64_aligned_t first_pfn;
+    /* Number of pages. */
+    uint64_aligned_t nr;
+};
+typedef struct xen_hvm_set_mem_type xen_hvm_set_mem_type_t;
+DEFINE_XEN_GUEST_HANDLE(xen_hvm_set_mem_type_t);
+
+
 #endif /* defined(__XEN__) || defined(__XEN_TOOLS__) */
 
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */