kvm: x86: refine kvm_get_arch_capabilities()

1. Using X86_FEATURE_ARCH_CAPABILITIES to enumerate the existence of
MSR_IA32_ARCH_CAPABILITIES to avoid using rdmsrl_safe().

2. Since kvm_get_arch_capabilities() is only used in this file, making
it static.
Signed-off-by: NXiaoyao Li <xiaoyao.li@linux.intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1532,7 +1532,6 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
 		    unsigned long ipi_bitmap_high, u32 min,
 		    unsigned long icr, int op_64_bit);
 
-u64 kvm_get_arch_capabilities(void);
 void kvm_define_shared_msr(unsigned index, u32 msr);
 int kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
 

arch/x86/kvm/x86.c

@@ -1212,11 +1212,12 @@ static u32 msr_based_features[] = {
 
 static unsigned int num_msr_based_features;
 
-u64 kvm_get_arch_capabilities(void)
+static u64 kvm_get_arch_capabilities(void)
 {
-	u64 data;
+	u64 data = 0;
 
-	rdmsrl_safe(MSR_IA32_ARCH_CAPABILITIES, &data);
+	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
+		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, data);
 
 	/*
 	 * If we're doing cache flushes (either "always" or "cond")
@@ -1232,7 +1233,6 @@ u64 kvm_get_arch_capabilities(void)
 
 	return data;
 }
-EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
 
 static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
 {