@@ -21,6 +21,7 @@
#define HYPERV_CPUID_FEATURES 0x40000003
#define HYPERV_CPUID_ENLIGHTMENT_INFO 0x40000004
#define HYPERV_CPUID_IMPLEMENT_LIMITS 0x40000005
+#define HYPERV_CPUID_CPU_MANAGEMENT_FEATURES 0x40000007
#define HYPERV_CPUID_NESTED_FEATURES 0x4000000A
#define HYPERV_CPUID_VIRT_STACK_INTERFACE 0x40000081
@@ -110,6 +111,15 @@
/* Recommend using enlightened VMCS */
#define HV_X64_ENLIGHTENED_VMCS_RECOMMENDED BIT(14)
+/*
+ * CPU management features identification.
+ * These are HYPERV_CPUID_CPU_MANAGEMENT_FEATURES.EAX bits.
+ */
+#define HV_X64_START_LOGICAL_PROCESSOR BIT(0)
+#define HV_X64_CREATE_ROOT_VIRTUAL_PROCESSOR BIT(1)
+#define HV_X64_PERFORMANCE_COUNTER_SYNC BIT(2)
+#define HV_X64_RESERVED_IDENTITY_BIT BIT(31)
+
/*
* Virtual processor will never share a physical core with another virtual
* processor, except for virtual processors that are reported as sibling SMT
@@ -198,6 +198,8 @@ int hyperv_fill_flush_guest_mapping_list(
struct hv_guest_mapping_flush_list *flush,
u64 start_gfn, u64 end_gfn);
+extern bool hv_root_partition;
+
#ifdef CONFIG_X86_64
void hv_apic_init(void);
void __init hv_init_spinlocks(void);
@@ -32,6 +32,10 @@
#include <asm/nmi.h>
#include <clocksource/hyperv_timer.h>
+/* Is Linux running as the root partition? */
+bool hv_root_partition;
+EXPORT_SYMBOL_GPL(hv_root_partition);
+
struct ms_hyperv_info ms_hyperv;
EXPORT_SYMBOL_GPL(ms_hyperv);
@@ -250,6 +254,22 @@ static void __init ms_hyperv_init_platform(void)
pr_debug("Hyper-V: max %u virtual processors, %u logical processors\n",
ms_hyperv.max_vp_index, ms_hyperv.max_lp_index);
+ /*
+ * Check CPU management privilege.
+ *
+ * To mirror what Windows does we should extract CPU management
+ * features and use the ReservedIdentityBit to detect if Linux is the
+ * root partition. But that requires negotiating CPU management
+ * interface (a process to be finalized).
+ *
+ * For now, use the privilege flag as the indicator for running as
+ * root.
+ */
+ if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_CPU_MANAGEMENT) {
+ hv_root_partition = true;
+ pr_info("Hyper-V: running as root partition\n");
+ }
+
/*
* Extract host information.
*/