[PATCH 2/2] KVM: x86: Add blurb to CPUID tracepoint when using max basic leaf values

[Sean Christopherson <sean.j.christopherson@xxxxxxxxx>]

Tack on "used max basic" at the end of the CPUID tracepoint when the
output values correspond to the max basic leaf, i.e. when emulating
Intel's out-of-range CPUID behavior.  Observing "cpuid entry not found"
in the tracepoint with non-zero output values is confusing for users
that aren't familiar with the out-of-range semantics, and qualifying the
"not found" case hopefully makes it clear that "found" means "found the
exact entry".

Suggested-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c |  9 ++++++---
 arch/x86/kvm/trace.h | 11 +++++++----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index bccaae0df668..a515a83c6f29 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -990,13 +990,15 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 {
 	u32 orig_function = *eax, function = *eax, index = *ecx;
 	struct kvm_cpuid_entry2 *entry;
-	bool exact;
+	bool exact, used_max_basic = false;
 
 	entry = kvm_find_cpuid_entry(vcpu, function, index);
 	exact = !!entry;
 
-	if (!entry && !exact_only)
+	if (!entry && !exact_only) {
 		entry = get_out_of_range_cpuid_entry(vcpu, &function, index);
+		used_max_basic = !!entry;
+	}
 
 	if (entry) {
 		*eax = entry->eax;
@@ -1026,7 +1028,8 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 			}
 		}
 	}
-	trace_kvm_cpuid(orig_function, index, *eax, *ebx, *ecx, *edx, exact);
+	trace_kvm_cpuid(orig_function, index, *eax, *ebx, *ecx, *edx, exact,
+			used_max_basic);
 	return exact;
 }
 EXPORT_SYMBOL_GPL(kvm_cpuid);
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 27270ba0f05f..c3d1e9f4a2c0 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -153,8 +153,8 @@ TRACE_EVENT(kvm_fast_mmio,
 TRACE_EVENT(kvm_cpuid,
 	TP_PROTO(unsigned int function, unsigned int index, unsigned long rax,
 		 unsigned long rbx, unsigned long rcx, unsigned long rdx,
-		 bool found),
-	TP_ARGS(function, index, rax, rbx, rcx, rdx, found),
+		 bool found, bool used_max_basic),
+	TP_ARGS(function, index, rax, rbx, rcx, rdx, found, used_max_basic),
 
 	TP_STRUCT__entry(
 		__field(	unsigned int,	function	)
@@ -164,6 +164,7 @@ TRACE_EVENT(kvm_cpuid,
 		__field(	unsigned long,	rcx		)
 		__field(	unsigned long,	rdx		)
 		__field(	bool,		found		)
+		__field(	bool,		used_max_basic	)
 	),
 
 	TP_fast_assign(
@@ -174,12 +175,14 @@ TRACE_EVENT(kvm_cpuid,
 		__entry->rcx		= rcx;
 		__entry->rdx		= rdx;
 		__entry->found		= found;
+		__entry->used_max_basic	= used_max_basic;
 	),
 
-	TP_printk("func %x idx %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
+	TP_printk("func %x idx %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s%s",
 		  __entry->function, __entry->index, __entry->rax,
 		  __entry->rbx, __entry->rcx, __entry->rdx,
-		  __entry->found ? "found" : "not found")
+		  __entry->found ? "found" : "not found",
+		  __entry->used_max_basic ? ", used max basic" : "")
 );
 
 #define AREG(x) { APIC_##x, "APIC_" #x }
-- 
2.24.1