Kernel: Detect and display CPUID hypervisor signature

Kernel/Arch/x86/Processor.h

@@ -173,6 +173,8 @@ public:
     void early_initialize(u32 cpu);
     void initialize(u32 cpu);
 
+    void detect_hypervisor();
+
     void idle_begin()
     {
         s_idle_cpu_mask.fetch_or(1u << m_cpu, AK::MemoryOrder::memory_order_relaxed);

Kernel/Arch/x86/common/Processor.cpp

@@ -349,6 +349,9 @@ UNMAP_AFTER_INIT void Processor::initialize(u32 cpu)
         else
             asm volatile("fnsave %0"
                          : "=m"(s_clean_fpu_state));
+
+        if (has_feature(CPUFeature::HYPERVISOR))
+            detect_hypervisor();
     }
 
     m_info = new ProcessorInfo(*this);
@@ -360,6 +363,21 @@ UNMAP_AFTER_INIT void Processor::initialize(u32 cpu)
     }
 }
 
+UNMAP_AFTER_INIT void Processor::detect_hypervisor()
+{
+    CPUID hypervisor_leaf_range(0x40000000);
+
+    // Get signature of hypervisor.
+    alignas(sizeof(u32)) char hypervisor_signature_buffer[13];
+    *reinterpret_cast<u32*>(hypervisor_signature_buffer) = hypervisor_leaf_range.ebx();
+    *reinterpret_cast<u32*>(hypervisor_signature_buffer + 4) = hypervisor_leaf_range.ecx();
+    *reinterpret_cast<u32*>(hypervisor_signature_buffer + 8) = hypervisor_leaf_range.edx();
+    hypervisor_signature_buffer[12] = '\0';
+    StringView hypervisor_signature(hypervisor_signature_buffer);
+
+    dmesgln("CPU[{}]: CPUID hypervisor signature '{}' ({:#x} {:#x} {:#x}), max leaf {:#x}", id(), hypervisor_signature, hypervisor_leaf_range.ebx(), hypervisor_leaf_range.ecx(), hypervisor_leaf_range.edx(), hypervisor_leaf_range.eax());
+}
+
 void Processor::write_raw_gdt_entry(u16 selector, u32 low, u32 high)
 {
     u16 i = (selector & 0xfffc) >> 3;