[xen master] x86/Intel: use host CPU policy for ARAT checking

[patchbot@xxxxxxx]

commit 894bd76179241a854c9d70a45abc3f68f369f525
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jan 20 09:01:29 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jan 20 09:01:29 2026 +0100

    x86/Intel: use host CPU policy for ARAT checking
    
    There's no need to invoke CPUID yet another time. However, as the host CPU
    policy is set up only shortly after init_intel() ran on the BSP, defer the
    logic to a pre-SMP initcall. This can't be (a new) one in cpu/intel.c
    though, as that's linked after acpi/cpu_idle.c (which is where we already
    need the feature set). Since opt_arat is local to the cpu/ subtree,
    introduce a new Intel-specific helper to hold the code needed.
    
    Further, as we assume symmetry anyway, use setup_force_cpu_cap() and hence
    limit the checking to the boot CPU.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
 xen/arch/x86/acpi/cpu_idle.c          |  3 +++
 xen/arch/x86/cpu/intel.c              | 10 ++++++----
 xen/arch/x86/include/asm/cpufeature.h |  3 +++
 xen/arch/x86/include/asm/processor.h  |  1 +
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index 7a87625077..0b3d0631dd 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -1666,6 +1666,9 @@ static int __init cf_check cpuidle_presmp_init(void)
 {
     void *cpu = (void *)(long)smp_processor_id();
 
+    if ( boot_cpu_data.vendor == X86_VENDOR_INTEL )
+        intel_init_arat();
+
     if ( !xen_cpuidle )
         return 0;
 
diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index b76797cb9a..7037f1f268 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -665,10 +665,6 @@ static void cf_check init_intel(struct cpuinfo_x86 *c)
                __set_bit(X86_FEATURE_NONSTOP_TSC, c->x86_capability);
                __set_bit(X86_FEATURE_TSC_RELIABLE, c->x86_capability);
        }
-       if ( opt_arat &&
-            ( c->cpuid_level >= 0x00000006 ) &&
-            ( cpuid_eax(0x00000006) & (1u<<2) ) )
-               __set_bit(X86_FEATURE_XEN_ARAT, c->x86_capability);
 
        if ((opt_cpu_info && !(c->apicid & (c->x86_num_siblings - 1))) ||
            c == &boot_cpu_data )
@@ -693,3 +689,9 @@ const struct cpu_dev __initconst_cf_clobber intel_cpu_dev = 
{
        .c_early_init   = early_init_intel,
        .c_init         = init_intel,
 };
+
+void __init intel_init_arat(void)
+{
+    if ( opt_arat && cpu_has_arat )
+        setup_force_cpu_cap(X86_FEATURE_XEN_ARAT);
+}
diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index 8423f54723..f45295d84e 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -176,6 +176,9 @@ static inline bool boot_cpu_has(unsigned int feat)
 #define cpu_has_fma4            boot_cpu_has(X86_FEATURE_FMA4)
 #define cpu_has_tbm             boot_cpu_has(X86_FEATURE_TBM)
 
+/* CPUID level 0x00000006.eax */
+#define cpu_has_arat            host_cpu_policy.basic.arat
+
 /* CPUID level 0x00000006.ecx */
 #define cpu_has_hw_feedback_cap host_cpu_policy.basic.hw_feedback_cap
 
diff --git a/xen/arch/x86/include/asm/processor.h 
b/xen/arch/x86/include/asm/processor.h
index cf614bd8c6..c37bd7a176 100644
--- a/xen/arch/x86/include/asm/processor.h
+++ b/xen/arch/x86/include/asm/processor.h
@@ -102,6 +102,7 @@ extern void setup_force_cpu_cap(unsigned int cap);
 extern bool is_forced_cpu_cap(unsigned int cap);
 extern void print_cpu_info(unsigned int cpu);
 extern void init_intel_cacheinfo(struct cpuinfo_x86 *c);
+extern void intel_init_arat(void);
 
 #define cpu_to_core(_cpu)   (cpu_data[_cpu].cpu_core_id)
 #define cpu_to_socket(_cpu) (cpu_data[_cpu].phys_proc_id)
--
generated by git-patchbot for /home/xen/git/xen.git#master