[PATCH 1/2] KVM: CPUID: Check limit first when emulating CPUID instruction

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

When limit checking is required, it should be executed first, which is
consistent with the CPUID specification.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 50 +++++++++++++++++++++++++-------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 22c2720cd948..866546b4d834 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -952,23 +952,33 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
 EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
 
 /*
- * If no match is found, check whether we exceed the vCPU's limit
- * and return the content of the highest valid _standard_ leaf instead.
- * This is to satisfy the CPUID specification.
+ * Based on CPUID specification, if leaf number exceeds the vCPU's limit,
+ * it should return the content of the highest valid _standard_ leaf instead.
+ * Note: *found is set true only means the queried leaf number doesn't exceed
+ * the maximum leaf number of basic or extented leaf.
  */
-static struct kvm_cpuid_entry2* check_cpuid_limit(struct kvm_vcpu *vcpu,
-                                                  u32 function, u32 index)
+static struct kvm_cpuid_entry2* cpuid_check_limit(struct kvm_vcpu *vcpu,
+                                                  u32 function, u32 index,
+						  bool *found)
 {
 	struct kvm_cpuid_entry2 *maxlevel;
 
 	maxlevel = kvm_find_cpuid_entry(vcpu, function & 0x80000000, 0);
-	if (!maxlevel || maxlevel->eax >= function)
+	if (!maxlevel)
 		return NULL;
-	if (function & 0x80000000) {
-		maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0);
-		if (!maxlevel)
-			return NULL;
+
+	if (maxlevel->eax >= function) {
+		if (found)
+			*found = true;
+		return kvm_find_cpuid_entry(vcpu, function, index);
 	}
+
+	if (function & 0x80000000)
+		maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0);
+
+	if (!maxlevel)
+		return NULL;
+
 	return kvm_find_cpuid_entry(vcpu, maxlevel->eax, index);
 }
 
@@ -977,26 +987,22 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 {
 	u32 function = *eax, index = *ecx;
 	struct kvm_cpuid_entry2 *best;
-	bool entry_found = true;
+	bool entry_found = false;
 
-	best = kvm_find_cpuid_entry(vcpu, function, index);
+	if (check_limit)
+		best = cpuid_check_limit(vcpu, function, index, &entry_found);
+	else
+		best = kvm_find_cpuid_entry(vcpu, function, index);
 
-	if (!best) {
-		entry_found = false;
-		if (!check_limit)
-			goto out;
-
-		best = check_cpuid_limit(vcpu, function, index);
-	}
-
-out:
 	if (best) {
 		*eax = best->eax;
 		*ebx = best->ebx;
 		*ecx = best->ecx;
 		*edx = best->edx;
-	} else
+	} else {
+		entry_found = false;
 		*eax = *ebx = *ecx = *edx = 0;
+	}
 	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, entry_found);
 	return entry_found;
 }
-- 
2.19.1