x86/hyperv: detect if Linux is the root partition

For now we can use the privilege flag to check. Stash the value to be
used later.

Put in a bunch of defines for future use when we want to have more
fine-grained detection.

Signed-off-by: Wei Liu <wei.liu@kernel.org>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210203150435.27941-3-wei.liu@kernel.org

diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index 6aed936e5e96206a85fafef941ef93bf9a8cdd44..e3a6a723d661da20797fc4d4c8ea20555d4a1684 100644 (file)
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h
@@ -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_ISOLATION_CONFIG          0x4000000C
 
@@ -111,6 +112,15 @@
 /* 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

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 30f76b96685799c7e95cfff039d265a1dc42dea0..4014a1ca2faea7d8e81bbb49b1f7cbb1175c9e31 100644 (file)
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -239,6 +239,8 @@ 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);

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index fc6cb84c9fe57b994df4a30c45b0fe8124b5f033..39a4b4509b87dbbf98f2ab3985459b16da740bbc 100644 (file)
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -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);
 
@@ -256,6 +260,22 @@ 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.
         */