x86/acrn: Introduce acrn_cpuid_base() and hypervisor feature bits

ACRN Hypervisor reports hypervisor features via CPUID leaf 0x40000001
which is similar to KVM. A VM can check if it's the privileged VM using
the feature bits. The Service VM is the only privileged VM by design.

Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Fengwei Yin <fengwei.yin@intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Yu Wang <yu1.wang@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210207031040.49576-4-shuo.a.liu@intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/acrn.h

@@ -2,7 +2,23 @@
 #ifndef _ASM_X86_ACRN_H
 #define _ASM_X86_ACRN_H
 
+/*
+ * This CPUID returns feature bitmaps in EAX.
+ * Guest VM uses this to detect the appropriate feature bit.
+ */
+#define	ACRN_CPUID_FEATURES		0x40000001
+/* Bit 0 indicates whether guest VM is privileged */
+#define	ACRN_FEATURE_PRIVILEGED_VM	BIT(0)
+
 void acrn_setup_intr_handler(void (*handler)(void));
 void acrn_remove_intr_handler(void);
 
+static inline u32 acrn_cpuid_base(void)
+{
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		return hypervisor_cpuid_base("ACRNACRNACRN", 0);
+
+	return 0;
+}
+
 #endif /* _ASM_X86_ACRN_H */

arch/x86/kernel/cpu/acrn.c

@@ -21,7 +21,7 @@
 
 static u32 __init acrn_detect(void)
 {
-	return hypervisor_cpuid_base("ACRNACRNACRN", 0);
+	return acrn_cpuid_base();
 }
 
 static void __init acrn_init_platform(void)