tools/libx[cl]: Don't use HVM_PARAM_PAE_ENABLED as a function parameter

HVM_PARAM_PAE_ENABLED is set and consumed by the toolstack only.  It is in
practice a complicated and non-standard way of passing a boolean parameter
into xc_cpuid_apply_policy().

This is silly.  Pass PAE as a regular parameter instead.

In libxl__cpuid_legacy(), leave a rather better explaination of why only HVM
guests have a choice in PAE setting.

No change in how a guest is constructed.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxc/include/xenctrl.h

@@ -1801,7 +1801,7 @@ int xc_cpuid_set(xc_interface *xch,
 int xc_cpuid_apply_policy(xc_interface *xch,
                           uint32_t domid,
                           const uint32_t *featureset,
-                          unsigned int nr_features);
+                          unsigned int nr_features, bool pae);
 int xc_mca_op(xc_interface *xch, struct xen_mc *mc);
 int xc_mca_op_inject_v2(xc_interface *xch, unsigned int flags,
                         xc_cpumap_t cpumap, unsigned int nr_cpus);

tools/libxc/xc_cpuid_x86.c

@@ -455,7 +455,8 @@ int xc_cpuid_set(
 }
 
 int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid,
-                          const uint32_t *featureset, unsigned int nr_features)
+                          const uint32_t *featureset, unsigned int nr_features,
+                          bool pae)
 {
     int rc;
     xc_dominfo_t di;
@@ -579,8 +580,6 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid,
     }
     else
     {
-        uint64_t val;
-
         /*
          * Topology for HVM guests is entirely controlled by Xen.  For now, we
          * hardcode APIC_ID = vcpu_id * 2 to give the illusion of no SMT.
@@ -634,15 +633,7 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid,
             break;
         }
 
-        /*
-         * HVM_PARAM_PAE_ENABLED is a parameter to this function, stashed in
-         * Xen.  Nothing else has ever taken notice of the value.
-         */
-        rc = xc_hvm_param_get(xch, domid, HVM_PARAM_PAE_ENABLED, &val);
-        if ( rc )
-            goto out;
-
-        p->basic.pae = val;
+        p->basic.pae = pae;
 
         /*
          * These settings are necessary to cause earlier HVM_PARAM_NESTEDHVM /

tools/libxl/libxl_cpuid.c

@@ -416,8 +416,22 @@ void libxl__cpuid_legacy(libxl_ctx *ctx, uint32_t domid,
     libxl_cpuid_policy_list cpuid = info->cpuid;
     int i;
     char *cpuid_res[4];
+    bool pae = true;
 
-    xc_cpuid_apply_policy(ctx->xch, domid, NULL, 0);
+    /*
+     * For PV guests, PAE is Xen-controlled (it is the 'p' that differentiates
+     * the xen-3.0-x86_32 and xen-3.0-x86_32p ABIs).  It is mandatory as Xen
+     * is 64bit only these days.
+     *
+     * For PVH guests, there is no top-level PAE control in the domain config,
+     * so is treated as always available.
+     *
+     * HVM guests get a top-level choice of whether PAE is available.
+     */
+    if (info->type == LIBXL_DOMAIN_TYPE_HVM)
+        pae = libxl_defbool_val(info->u.hvm.pae);
+
+    xc_cpuid_apply_policy(ctx->xch, domid, NULL, 0, pae);
 
     if (!cpuid)
         return;