[PATCH v4 3/3] x86/CPUID: move bounding of max_{,sub}leaf fields to library code

[Jan Beulich <jbeulich@xxxxxxxx>]

Break out this logic from calculate_host_policy() to also use it in the
x86 emulator harness, where subsequently we'll want to avoid open-coding
AMX maximum palette bounding as well as AVX10 sub-feature pruning.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v4: Mark x86_cpu_policy_bound_max_leaves() __init. Add U suffixes.
    Re-base.
v2: New.

--- a/tools/tests/x86_emulator/x86-emulate.c
+++ b/tools/tests/x86_emulator/x86-emulate.c
@@ -76,6 +76,7 @@ bool emul_test_init(void)
     unsigned long sp;
 
     x86_cpu_policy_fill_native(&cp);
+    x86_cpu_policy_bound_max_leaves(&cp);
 
     /*
      * The emulator doesn't use these instructions, so can always emulate
@@ -89,6 +90,8 @@ bool emul_test_init(void)
     cp.feat.wrmsrns = true;
     cp.extd.clzero = true;
 
+    x86_cpu_policy_shrink_max_leaves(&cp);
+
     if ( cpu_has_xsave )
     {
         unsigned int tmp, ebx;
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -360,28 +360,19 @@ void calculate_raw_cpu_policy(void)
 static void __init calculate_host_policy(void)
 {
     struct cpu_policy *p = &host_cpu_policy;
-    unsigned int max_extd_leaf;
 
     *p = raw_cpu_policy;
 
-    p->basic.max_leaf =
-        min_t(uint32_t, p->basic.max_leaf,   ARRAY_SIZE(p->basic.raw) - 1);
-    p->feat.max_subleaf =
-        min_t(uint32_t, p->feat.max_subleaf, ARRAY_SIZE(p->feat.raw) - 1);
-
-    max_extd_leaf = p->extd.max_leaf;
-
     /*
      * For AMD/Hygon hardware before Zen3, we unilaterally modify LFENCE to be
      * dispatch serialising for Spectre mitigations.  Extend max_extd_leaf
      * beyond what hardware supports, to include the feature leaf containing
      * this information.
      */
-    if ( cpu_has_lfence_dispatch )
-        max_extd_leaf = max(max_extd_leaf, 0x80000021U);
+    if ( cpu_has_lfence_dispatch && p->extd.max_leaf < 0x80000021U )
+        p->extd.max_leaf = 0x80000021U;
 
-    p->extd.max_leaf = 0x80000000U | min_t(uint32_t, max_extd_leaf & 0xffff,
-                                           ARRAY_SIZE(p->extd.raw) - 1);
+    x86_cpu_policy_bound_max_leaves(p);
 
     x86_cpu_featureset_to_policy(boot_cpu_data.x86_capability, p);
     recalculate_xstate(p);
--- a/xen/include/xen/lib/x86/cpu-policy.h
+++ b/xen/include/xen/lib/x86/cpu-policy.h
@@ -439,6 +439,12 @@ void x86_cpu_policy_fill_native(struct c
 void x86_cpu_policy_clear_out_of_range_leaves(struct cpu_policy *p);
 
 /**
+ * Bound max leaf/subleaf values according to the capacity of the respective
+ * arrays in struct cpu_policy.
+ */
+void x86_cpu_policy_bound_max_leaves(struct cpu_policy *p);
+
+/**
  * Shrink max leaf/subleaf values such that the last respective valid entry
  * isn't all blank.  While permitted by the spec, such extraneous leaves may
  * provide undue "hints" to guests.
--- a/xen/lib/x86/cpuid.c
+++ b/xen/lib/x86/cpuid.c
@@ -291,6 +291,16 @@ void x86_cpu_policy_clear_out_of_range_l
                 ARRAY_SIZE(p->extd.raw) - 1);
 }
 
+void __init x86_cpu_policy_bound_max_leaves(struct cpu_policy *p)
+{
+    p->basic.max_leaf =
+        min_t(uint32_t, p->basic.max_leaf, ARRAY_SIZE(p->basic.raw) - 1);
+    p->feat.max_subleaf =
+        min_t(uint32_t, p->feat.max_subleaf, ARRAY_SIZE(p->feat.raw) - 1);
+    p->extd.max_leaf = 0x80000000U | min_t(uint32_t, p->extd.max_leaf & 0xffff,
+                                           ARRAY_SIZE(p->extd.raw) - 1);
+}
+
 void x86_cpu_policy_shrink_max_leaves(struct cpu_policy *p)
 {
     unsigned int i;
--- a/xen/lib/x86/private.h
+++ b/xen/lib/x86/private.h
@@ -5,6 +5,7 @@
 
 #include <xen/bitops.h>
 #include <xen/guest_access.h>
+#include <xen/init.h>
 #include <xen/kernel.h>
 #include <xen/lib.h>
 #include <xen/nospec.h>
@@ -28,6 +29,11 @@
 
 #include <xen-tools/common-macros.h>
 
+#define __init
+#define __initdata
+#define __initconst
+#define __initconstrel
+
 static inline bool test_bit(unsigned int bit, const void *vaddr)
 {
     const char *addr = vaddr;