x86, kvm: cache the base of the KVM cpuid leaves

It is unnecessary to go through hypervisor_cpuid_base every time
a leaf is found (which will be every time a feature is requested
after the next patch).

Fixes: 1085ba7f552d84aa8ac0ae903fa8d0cc2ff9f79d
Cc: stable@vger.kernel.org
Cc: mtosatti@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 33 insertions, 16 deletions

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 1df115909758..1679cc799b26 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -85,28 +85,13 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
         return ret;
 }
 
-static inline uint32_t kvm_cpuid_base(void)
-{
-        if (boot_cpu_data.cpuid_level < 0)
-                return 0;       /* So we don't blow up on old processors */
-
-        if (cpu_has_hypervisor)
-                return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
-
-        return 0;
-}
-
-static inline bool kvm_para_available(void)
-{
-        return kvm_cpuid_base() != 0;
-}
-
 static inline unsigned int kvm_arch_para_features(void)
 {
         return cpuid_eax(KVM_CPUID_FEATURES);
 }
 
 #ifdef CONFIG_KVM_GUEST
+bool kvm_para_available(void);
 void __init kvm_guest_init(void);
 void kvm_async_pf_task_wait(u32 token);
 void kvm_async_pf_task_wake(u32 token);
@@ -126,6 +111,11 @@ static inline void kvm_spinlock_init(void)
 #define kvm_async_pf_task_wait(T) do {} while(0)
 #define kvm_async_pf_task_wake(T) do {} while(0)
 
+static inline bool kvm_para_available(void)
+{
+        return 0;
+}
+
 static inline u32 kvm_read_and_reset_pf_reason(void)
 {
         return 0;
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 6dd802c6d780..0823003770fc 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -500,6 +500,33 @@ void __init kvm_guest_init(void)
 #endif
 }
 
+static noinline uint32_t __kvm_cpuid_base(void)
+{
+        if (boot_cpu_data.cpuid_level < 0)
+                return 0;       /* So we don't blow up on old processors */
+
+        if (cpu_has_hypervisor)
+                return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
+
+        return 0;
+}
+
+static inline uint32_t kvm_cpuid_base(void)
+{
+        static int kvm_cpuid_base = -1;
+
+        if (kvm_cpuid_base == -1)
+                kvm_cpuid_base = __kvm_cpuid_base();
+
+        return kvm_cpuid_base;
+}
+
+bool kvm_para_available(void)
+{
+        return kvm_cpuid_base() != 0;
+}
+EXPORT_SYMBOL_GPL(kvm_para_available);
+
 static uint32_t __init kvm_detect(void)
 {
         return kvm_cpuid_base();