[PATCH v3 for-4.22] x86/cpu-policy: set up host policy earlier

[Jan Beulich <jbeulich@xxxxxxxx>]

In order to use cpu_has_* expanding to host_cpu_policy.*, the host policy
needs setting up alongside boot_cpu_data.x86_capability[]. Arrange for
that towards the end of identify_cpu(). Then make sure .x86_capability[]
and host policy remain in sync when setup_{force,clear}_cpu_cap() are
used.

Rename the function now it's no longer static.

Fixes: 894bd7617924 ("x86/Intel: use host CPU policy for ARAT checking")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
This really was part of one of the XSTATE cleanup patches at the head of
the AMX series. This explains the specific placement ahead of the call to
xstate_init()). Likely anything from there downwards shouldn't really
live in identify_cpu() anyway.
---
v3: Make call from setup_force_cpu_cap() conditional.
v2: Call calculate_host_cpu_policy() from setup_{force,clear}_cpu_cap()
    instead of from init_guest_cpu_policies().

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -66,8 +66,10 @@ void __init setup_clear_cpu_cap(unsigned
        __clear_bit(cap, boot_cpu_data.x86_capability);
        dfs = x86_cpu_policy_lookup_deep_deps(cap);
 
-       if (!dfs)
+       if (!dfs) {
+               calculate_host_cpu_policy();
                return;
+       }
 
        for (i = 0; i < FSCAPINTS; ++i) {
                cleared_caps[i] |= dfs[i];
@@ -78,6 +80,8 @@ void __init setup_clear_cpu_cap(unsigned
                       __builtin_return_address(0),
                       i, forced_caps[i] & dfs[i]);
        }
+
+       calculate_host_cpu_policy();
 }
 
 void __init setup_force_cpu_cap(unsigned int cap)
@@ -92,6 +96,10 @@ void __init setup_force_cpu_cap(unsigned
        }
 
        __set_bit(cap, boot_cpu_data.x86_capability);
+
+       /* Don't recalculate when the bit isn't represented in the policy. */
+       if (cap < FSCAPINTS * 32)
+               calculate_host_cpu_policy();
 }
 
 bool __init is_forced_cpu_cap(unsigned int cap)
@@ -586,6 +594,8 @@ void identify_cpu(struct cpuinfo_x86 *c)
        }
 
        /* Now the feature flags better reflect actual CPU features! */
+       if (c == &boot_cpu_data)
+               calculate_host_cpu_policy();
 
        xstate_init(c);
 
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -359,11 +359,18 @@ void calculate_raw_cpu_policy(void)
     /* Was already added by probe_cpuid_faulting() */
 }
 
-static void __init calculate_host_policy(void)
+void __init calculate_host_cpu_policy(void)
 {
     struct cpu_policy *p = &host_cpu_policy;
     unsigned int max_extd_leaf;
 
+    /*
+     * Bail if the raw policy wasn't set up yet. At least recalculate_xstate()
+     * can't be used yet in that case.
+     */
+    if ( !raw_cpu_policy.basic.max_leaf )
+        return;
+
     *p = raw_cpu_policy;
 
     p->basic.max_leaf =
@@ -904,8 +911,6 @@ static void __init calculate_hvm_def_pol
 
 void __init init_guest_cpu_policies(void)
 {
-    calculate_host_policy();
-
     if ( IS_ENABLED(CONFIG_PV) )
     {
         calculate_pv_max_policy();
--- a/xen/arch/x86/include/asm/cpu-policy.h
+++ b/xen/arch/x86/include/asm/cpu-policy.h
@@ -30,4 +30,10 @@ void recalculate_cpuid_policy(struct dom
  */
 void calculate_raw_cpu_policy(void);
 
+/*
+ * Collect the host CPU policy.  Called after collecting enough CPUID output,
+ * and again after all feature overrides have been put in place.
+ */
+void calculate_host_cpu_policy(void);
+
 #endif /* X86_CPU_POLICY_H */