[xen master] x86/cpu-policy: set up host policy earlier

[patchbot@xxxxxxx]

commit aa2f6c99f3b7d2babbe21cdf81a6e5656583e242
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Jul 29 16:02:31 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jul 29 16:02:31 2026 +0200

    x86/cpu-policy: set up host policy earlier
    
    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>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/x86/cpu-policy.c             | 11 ++++++++---
 xen/arch/x86/cpu/common.c             | 12 +++++++++++-
 xen/arch/x86/include/asm/cpu-policy.h |  6 ++++++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index 5273fe0ae4..eddcd9778f 100644
--- 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_policy(void)
 
 void __init init_guest_cpu_policies(void)
 {
-    calculate_host_policy();
-
     if ( IS_ENABLED(CONFIG_PV) )
     {
         calculate_pv_max_policy();
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index fe8a818c1b..771ec2cf86 100644
--- 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 int cap)
        __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 int cap)
                       __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 int cap)
        }
 
        __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);
 
diff --git a/xen/arch/x86/include/asm/cpu-policy.h 
b/xen/arch/x86/include/asm/cpu-policy.h
index 99d5a8e67e..943407963a 100644
--- 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 domain *d);
  */
 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 */
--
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