[PATCH] libxg: don't use max policy in xc_cpuid_xend_policy()

[Jan Beulich <jbeulich@xxxxxxxx>]

Using max undermines the separation between default and max. For example,
turning off AVX512F on an MPX-capable system silently turns on MPX,
despite this not being part of the default policy anymore. Since the
information is used only for determining what to convert 'x' to (but not
to e.g. validate '1' settings), the effect of this change is identical
for guests with (suitable) "cpuid=" settings to that of the changes
separating default from max and then converting (e.g.) MPX from being
part of default to only being part of max for guests without (affected)
"cpuid=" settings.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -288,11 +288,11 @@ static int xc_cpuid_xend_policy(
     unsigned int nr_leaves, nr_msrs;
     uint32_t err_leaf = -1, err_subleaf = -1, err_msr = -1;
     /*
-     * Three full policies.  The host, domain max, and domain current for the
-     * domain type.
+     * Three full policies.  The host, default for the domain type,
+     * and domain current.
      */
-    xen_cpuid_leaf_t *host = NULL, *max = NULL, *cur = NULL;
-    unsigned int nr_host, nr_max, nr_cur;
+    xen_cpuid_leaf_t *host = NULL, *def = NULL, *cur = NULL;
+    unsigned int nr_host, nr_def, nr_cur;
 
     if ( xc_domain_getinfo(xch, domid, 1, &di) != 1 ||
          di.domid != domid )
@@ -312,7 +312,7 @@ static int xc_cpuid_xend_policy(
 
     rc = -ENOMEM;
     if ( (host = calloc(nr_leaves, sizeof(*host))) == NULL ||
-         (max  = calloc(nr_leaves, sizeof(*max)))  == 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);
@@ -330,15 +330,16 @@ static int xc_cpuid_xend_policy(
         goto fail;
     }
 
-    /* Get the domain's max policy. */
+    /* Get the domain type's default policy. */
     nr_msrs = 0;
-    nr_max = nr_leaves;
-    rc = xc_get_system_cpu_policy(xch, di.hvm ? XEN_SYSCTL_cpu_policy_hvm_max
-                                              : XEN_SYSCTL_cpu_policy_pv_max,
-                                  &nr_max, max, &nr_msrs, NULL);
+    nr_def = nr_leaves;
+    rc = xc_get_system_cpu_policy(xch,
+                                  di.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 max policy", di.hvm ? "hvm" : "pv");
+        PERROR("Failed to obtain %s def policy", di.hvm ? "hvm" : "pv");
         rc = -errno;
         goto fail;
     }
@@ -359,10 +360,10 @@ static int xc_cpuid_xend_policy(
     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 *max_leaf = find_leaf(max, nr_max, 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);
 
-        if ( cur_leaf == NULL || max_leaf == NULL || host_leaf == NULL )
+        if ( cur_leaf == NULL || def_leaf == NULL || host_leaf == NULL )
         {
             ERROR("Missing leaf %#x, subleaf %#x", xend->leaf, xend->subleaf);
             goto fail;
@@ -371,7 +372,7 @@ static int xc_cpuid_xend_policy(
         for ( unsigned int i = 0; i < ARRAY_SIZE(xend->policy); i++ )
         {
             uint32_t *cur_reg = &cur_leaf->a + i;
-            const uint32_t *max_reg = &max_leaf->a + i;
+            const uint32_t *def_reg = &def_leaf->a + i;
             const uint32_t *host_reg = &host_leaf->a + i;
 
             if ( xend->policy[i] == NULL )
@@ -386,7 +387,7 @@ static int xc_cpuid_xend_policy(
                 else if ( xend->policy[i][j] == '0' )
                     val = false;
                 else if ( xend->policy[i][j] == 'x' )
-                    val = test_bit(31 - j, max_reg);
+                    val = test_bit(31 - j, def_reg);
                 else if ( xend->policy[i][j] == 'k' ||
                           xend->policy[i][j] == 's' )
                     val = test_bit(31 - j, host_reg);
@@ -419,7 +420,7 @@ static int xc_cpuid_xend_policy(
 
  fail:
     free(cur);
-    free(max);
+    free(def);
     free(host);
 
     return rc;