1 files changed, 30 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 824aee0117bb..348cf4821240 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1749,3 +1749,33 @@ static int __init init_cpu_syscore(void)
         return 0;
 }
 core_initcall(init_cpu_syscore);
+
+/*
+ * The microcode loader calls this upon late microcode load to recheck features,
+ * only when microcode has been updated. Caller holds microcode_mutex and CPU
+ * hotplug lock.
+ */
+void microcode_check(void)
+{
+        struct cpuinfo_x86 info;
+
+        perf_check_microcode();
+
+        /* Reload CPUID max function as it might've changed. */
+        info.cpuid_level = cpuid_eax(0);
+
+        /*
+         * Copy all capability leafs to pick up the synthetic ones so that
+         * memcmp() below doesn't fail on that. The ones coming from CPUID will
+         * get overwritten in get_cpu_cap().
+         */
+        memcpy(&info.x86_capability, &boot_cpu_data.x86_capability, sizeof(info.x86_capability));
+
+        get_cpu_cap(&info);
+
+        if (!memcmp(&info.x86_capability, &boot_cpu_data.x86_capability, sizeof(info.x86_capability)))
+                return;
+
+        pr_warn("x86/CPU: CPU features have changed after loading microcode, but might not take effect.\n");
+        pr_warn("x86/CPU: Please consider either early loading through initrd/built-in or a potential BIOS update.\n");
+}