[PATCH v4 03/17] x86/acrn: Introduce an API to check if a VM is privileged

[shuo . a . liu]

From: Yin Fengwei <fengwei.yin@xxxxxxxxx>

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.

Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Signed-off-by: Shuo Liu <shuo.a.liu@xxxxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Fengwei Yin <fengwei.yin@xxxxxxxxx>
Cc: Zhi Wang <zhi.a.wang@xxxxxxxxx>
Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
Cc: Yu Wang <yu1.wang@xxxxxxxxx>
Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/acrn.h |  9 +++++++++
 arch/x86/kernel/cpu/acrn.c  | 19 ++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/acrn.h b/arch/x86/include/asm/acrn.h
index ff259b69cde7..a2d4aea3a80d 100644
--- a/arch/x86/include/asm/acrn.h
+++ b/arch/x86/include/asm/acrn.h
@@ -2,7 +2,16 @@
 #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);
+bool acrn_is_privileged_vm(void);
 
 #endif /* _ASM_X86_ACRN_H */
diff --git a/arch/x86/kernel/cpu/acrn.c b/arch/x86/kernel/cpu/acrn.c
index 42e88d01ccf9..b04fef8bd50b 100644
--- a/arch/x86/kernel/cpu/acrn.c
+++ b/arch/x86/kernel/cpu/acrn.c
@@ -21,9 +21,26 @@
 #include <asm/idtentry.h>
 #include <asm/irq_regs.h>
 
+static u32 acrn_cpuid_base(void)
+{
+	static u32 acrn_cpuid_base;
+
+	if (!acrn_cpuid_base && boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		acrn_cpuid_base = hypervisor_cpuid_base("ACRNACRNACRN", 0);
+
+	return acrn_cpuid_base;
+}
+
+bool acrn_is_privileged_vm(void)
+{
+	return cpuid_eax(acrn_cpuid_base() | ACRN_CPUID_FEATURES) &
+			 ACRN_FEATURE_PRIVILEGED_VM;
+}
+EXPORT_SYMBOL_GPL(acrn_is_privileged_vm);
+
 static u32 __init acrn_detect(void)
 {
-	return hypervisor_cpuid_base("ACRNACRNACRN", 0);
+	return acrn_cpuid_base();
 }
 
 static void __init acrn_init_platform(void)
-- 
2.28.0