diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index acc94fb16b..e2a2659953 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -312,102 +312,32 @@ static int compare_leaves(const void *l, const void *r)
     return 0;
 }
 
-static xen_cpuid_leaf_t *find_leaf(
-    xen_cpuid_leaf_t *leaves, unsigned int nr_leaves,
-    const struct xc_xend_cpuid *xend)
+static xen_cpuid_leaf_t *find_leaf(xc_cpu_policy_t *p,
+                                   const struct xc_xend_cpuid *xend)
 {
     const xen_cpuid_leaf_t key = { xend->leaf, xend->subleaf };
 
-    return bsearch(&key, leaves, nr_leaves, sizeof(*leaves), compare_leaves);
+    return bsearch(&key, p->leaves.buf, p->leaves.len,
+                   sizeof(*p->leaves.buf), compare_leaves);
 }
 
 static int xc_cpuid_xend_policy(
-    xc_interface *xch, uint32_t domid, const struct xc_xend_cpuid *xend)
+    xc_interface *xch, uint32_t domid,
+    const struct xc_xend_cpuid *xend,
+    xc_cpu_policy_t *host,
+    xc_cpu_policy_t *def,
+    xc_cpu_policy_t *cur)
 {
-    int rc;
-    bool hvm;
-    xc_domaininfo_t di;
-    unsigned int nr_leaves, nr_msrs;
-    uint32_t err_leaf = -1, err_subleaf = -1, err_msr = -1;
-    /*
-     * Three full policies.  The host, default for the domain type,
-     * and domain current.
-     */
-    xen_cpuid_leaf_t *host = NULL, *def = NULL, *cur = NULL;
-    unsigned int nr_host, nr_def, nr_cur;
-
-    if ( (rc = xc_domain_getinfo_single(xch, domid, &di)) < 0 )
-    {
-        PERROR("Failed to obtain d%d info", domid);
-        rc = -errno;
-        goto fail;
-    }
-    hvm = di.flags & XEN_DOMINF_hvm_guest;
-
-    rc = xc_cpu_policy_get_size(xch, &nr_leaves, &nr_msrs);
-    if ( rc )
-    {
-        PERROR("Failed to obtain policy info size");
-        rc = -errno;
-        goto fail;
-    }
-
-    rc = -ENOMEM;
-    if ( (host = calloc(nr_leaves, sizeof(*host))) == NULL ||
-         (def  = calloc(nr_leaves, sizeof(*def)))  == NULL ||
-         (cur  = calloc(nr_leaves, sizeof(*cur)))  == NULL )
-    {
-        ERROR("Unable to allocate memory for %u CPUID leaves", nr_leaves);
-        goto fail;
-    }
-
-    /* Get the domain's current policy. */
-    nr_msrs = 0;
-    nr_cur = nr_leaves;
-    rc = get_domain_cpu_policy(xch, domid, &nr_cur, cur, &nr_msrs, NULL);
-    if ( rc )
-    {
-        PERROR("Failed to obtain d%d current policy", domid);
-        rc = -errno;
-        goto fail;
-    }
-
-    /* Get the domain type's default policy. */
-    nr_msrs = 0;
-    nr_def = nr_leaves;
-    rc = get_system_cpu_policy(xch, hvm ? XEN_SYSCTL_cpu_policy_hvm_default
-                                        : XEN_SYSCTL_cpu_policy_pv_default,
-                               &nr_def, def, &nr_msrs, NULL);
-    if ( rc )
-    {
-        PERROR("Failed to obtain %s def policy", hvm ? "hvm" : "pv");
-        rc = -errno;
-        goto fail;
-    }
-
-    /* Get the host policy. */
-    nr_msrs = 0;
-    nr_host = nr_leaves;
-    rc = get_system_cpu_policy(xch, XEN_SYSCTL_cpu_policy_host,
-                               &nr_host, host, &nr_msrs, NULL);
-    if ( rc )
-    {
-        PERROR("Failed to obtain host policy");
-        rc = -errno;
-        goto fail;
-    }
-
-    rc = -EINVAL;
     for ( ; xend->leaf != XEN_CPUID_INPUT_UNUSED; ++xend )
     {
-        xen_cpuid_leaf_t *cur_leaf = find_leaf(cur, nr_cur, xend);
-        const xen_cpuid_leaf_t *def_leaf = find_leaf(def, nr_def, xend);
-        const xen_cpuid_leaf_t *host_leaf = find_leaf(host, nr_host, xend);
+        xen_cpuid_leaf_t *cur_leaf = find_leaf(cur, xend);
+        const xen_cpuid_leaf_t *def_leaf = find_leaf(def, xend);
+        const xen_cpuid_leaf_t *host_leaf = find_leaf(host, xend);
 
         if ( cur_leaf == NULL || def_leaf == NULL || host_leaf == NULL )
         {
             ERROR("Missing leaf %#x, subleaf %#x", xend->leaf, xend->subleaf);
-            goto fail;
+            return -EINVAL;
         }
 
         for ( unsigned int i = 0; i < ARRAY_SIZE(xend->policy); i++ )
@@ -436,7 +366,7 @@ static int xc_cpuid_xend_policy(
                 {
                     ERROR("Bad character '%c' in policy[%d] string '%s'",
                           xend->policy[i][j], i, xend->policy[i]);
-                    goto fail;
+                    return -EINVAL;
                 }
 
                 clear_bit(31 - j, cur_reg);
@@ -446,25 +376,7 @@ static int xc_cpuid_xend_policy(
         }
     }
 
-    /* Feed the transformed currrent policy back up to Xen. */
-    rc = xc_set_domain_cpu_policy(xch, domid, nr_cur, cur, 0, NULL,
-                                  &err_leaf, &err_subleaf, &err_msr);
-    if ( rc )
-    {
-        PERROR("Failed to set d%d's policy (err leaf %#x, subleaf %#x, msr %#x)",
-               domid, err_leaf, err_subleaf, err_msr);
-        rc = -errno;
-        goto fail;
-    }
-
-    /* Success! */
-
- fail:
-    free(cur);
-    free(def);
-    free(host);
-
-    return rc;
+    return 0;
 }
 
 static int compare_msr(const void *l, const void *r)
@@ -478,104 +390,31 @@ static int compare_msr(const void *l, const void *r)
     return lhs->idx < rhs->idx ? -1 : 1;
 }
 
-static xen_msr_entry_t *find_msr(
-    xen_msr_entry_t *msrs, unsigned int nr_msrs,
-    uint32_t index)
+static xen_msr_entry_t *find_msr(xc_cpu_policy_t *p, uint32_t index)
 {
     const xen_msr_entry_t key = { .idx = index };
 
-    return bsearch(&key, msrs, nr_msrs, sizeof(*msrs), compare_msr);
+    return bsearch(&key, p->msrs.buf, p->msrs.len,
+                   sizeof(*p->msrs.buf), compare_msr);
 }
 
-
 static int xc_msr_policy(xc_interface *xch, domid_t domid,
-                         const struct xc_msr *msr)
+                         const struct xc_msr *msr,
+                         xc_cpu_policy_t *host,
+                         xc_cpu_policy_t *def,
+                         xc_cpu_policy_t *cur)
 {
-    int rc;
-    bool hvm;
-    xc_domaininfo_t di;
-    unsigned int nr_leaves, nr_msrs;
-    uint32_t err_leaf = -1, err_subleaf = -1, err_msr = -1;
-    /*
-     * Three full policies.  The host, default for the domain type,
-     * and domain current.
-     */
-    xen_msr_entry_t *host = NULL, *def = NULL, *cur = NULL;
-    unsigned int nr_host, nr_def, nr_cur;
-
-    if ( (rc = xc_domain_getinfo_single(xch, domid, &di)) < 0 )
-    {
-        PERROR("Failed to obtain d%d info", domid);
-        rc = -errno;
-        goto out;
-    }
-    hvm = di.flags & XEN_DOMINF_hvm_guest;
-
-    rc = xc_cpu_policy_get_size(xch, &nr_leaves, &nr_msrs);
-    if ( rc )
-    {
-        PERROR("Failed to obtain policy info size");
-        rc = -errno;
-        goto out;
-    }
-
-    if ( (host = calloc(nr_msrs, sizeof(*host))) == NULL ||
-         (def  = calloc(nr_msrs, sizeof(*def)))  == NULL ||
-         (cur  = calloc(nr_msrs, sizeof(*cur)))  == NULL )
-    {
-        ERROR("Unable to allocate memory for %u CPUID leaves", nr_leaves);
-        rc = -ENOMEM;
-        goto out;
-    }
-
-    /* Get the domain's current policy. */
-    nr_leaves = 0;
-    nr_cur = nr_msrs;
-    rc = get_domain_cpu_policy(xch, domid, &nr_leaves, NULL, &nr_cur, cur);
-    if ( rc )
-    {
-        PERROR("Failed to obtain d%d current policy", domid);
-        rc = -errno;
-        goto out;
-    }
-
-    /* Get the domain type's default policy. */
-    nr_leaves = 0;
-    nr_def = nr_msrs;
-    rc = get_system_cpu_policy(xch, hvm ? XEN_SYSCTL_cpu_policy_hvm_default
-                                        : XEN_SYSCTL_cpu_policy_pv_default,
-                               &nr_leaves, NULL, &nr_def, def);
-    if ( rc )
-    {
-        PERROR("Failed to obtain %s def policy", hvm ? "hvm" : "pv");
-        rc = -errno;
-        goto out;
-    }
-
-    /* Get the host policy. */
-    nr_leaves = 0;
-    nr_host = nr_msrs;
-    rc = get_system_cpu_policy(xch, XEN_SYSCTL_cpu_policy_host,
-                               &nr_leaves, NULL, &nr_host, host);
-    if ( rc )
-    {
-        PERROR("Failed to obtain host policy");
-        rc = -errno;
-        goto out;
-    }
-
     for ( ; msr->index != XC_MSR_INPUT_UNUSED; ++msr )
     {
-        xen_msr_entry_t *cur_msr = find_msr(cur, nr_cur, msr->index);
-        const xen_msr_entry_t *def_msr = find_msr(def, nr_def, msr->index);
-        const xen_msr_entry_t *host_msr = find_msr(host, nr_host, msr->index);
+        xen_msr_entry_t *cur_msr = find_msr(cur, msr->index);
+        const xen_msr_entry_t *def_msr = find_msr(def, msr->index);
+        const xen_msr_entry_t *host_msr = find_msr(host, msr->index);
         unsigned int i;
 
         if ( cur_msr == NULL || def_msr == NULL || host_msr == NULL )
         {
             ERROR("Missing MSR %#x", msr->index);
-            rc = -ENOENT;
-            goto out;
+            return -ENOENT;
         }
 
         for ( i = 0; i < ARRAY_SIZE(msr->policy) - 1; i++ )
@@ -594,8 +433,7 @@ static int xc_msr_policy(xc_interface *xch, domid_t domid,
             {
                 ERROR("MSR index %#x: bad character '%c' in policy string '%s'",
                       msr->index, msr->policy[i], msr->policy);
-                rc = -EINVAL;
-                goto out;
+                return -EINVAL;
             }
 
             if ( val )
@@ -605,25 +443,7 @@ static int xc_msr_policy(xc_interface *xch, domid_t domid,
         }
     }
 
-    /* Feed the transformed policy back up to Xen. */
-    rc = xc_set_domain_cpu_policy(xch, domid, 0, NULL, nr_cur, cur,
-                                  &err_leaf, &err_subleaf, &err_msr);
-    if ( rc )
-    {
-        PERROR("Failed to set d%d's policy (err leaf %#x, subleaf %#x, msr %#x)",
-               domid, err_leaf, err_subleaf, err_msr);
-        rc = -errno;
-        goto out;
-    }
-
-    /* Success! */
-
- out:
-    free(cur);
-    free(def);
-    free(host);
-
-    return rc;
+    return 0;
 }
 
 int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
@@ -822,25 +642,20 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
         }
     }
 
-    /* Re-apply the mutated policy onto the domain */
-    rc = xc_cpu_policy_set_domain(xch, domid, cur);
-    if ( rc )
-    {
-        rc = -errno;
+    /*
+     * Ensure changes we just made are reflected in the serialised form of
+     * the policy, as otherwise they they will be missed by the xend overrides
+     */
+    if ( (rc = cpu_policy_serialise_on_self(xch, cur)) )
         goto out;
-    }
 
-    if ( xend && (rc = xc_cpuid_xend_policy(xch, domid, xend)) )
+    /* Apply xend-style overrides */
+    if ( (xend && (rc = xc_cpuid_xend_policy(xch, domid, xend, host, def, cur))) ||
+         (msr && (rc = xc_msr_policy(xch, domid, msr, host, def, cur))) )
         goto out;
 
-    if ( msr )
-    {
-        rc = xc_msr_policy(xch, domid, msr);
-        if ( rc )
-            goto out;
-    }
-
-    rc = 0;
+    /* Re-apply the mutated policy onto the domain */
+    rc = xc_cpu_policy_set_domain_from_serialised(xch, domid, cur);
 
 out:
     xc_cpu_policy_destroy(cur);
