KVM: x86: Add requested index to the CPUID tracepoint

Output the requested index when tracing CPUID emulation; it's basically
mandatory for leafs where the index is meaningful, and is helpful for
verifying KVM correctness even when the index isn't meaningful, e.g. the
trace for a Linux guest's hypervisor_cpuid_base() probing appears to
be broken (returns all zeroes) at first glance, but is correct because
the index is non-zero, i.e. the output values correspond to a random
index in the maximum basic leaf.

Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -1026,7 +1026,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 			}
 		}
 	}
-	trace_kvm_cpuid(orig_function, *eax, *ebx, *ecx, *edx, exact);
+	trace_kvm_cpuid(orig_function, index, *eax, *ebx, *ecx, *edx, exact);
 	return exact;
 }
 EXPORT_SYMBOL_GPL(kvm_cpuid);

arch/x86/kvm/trace.h

@@ -151,12 +151,14 @@ TRACE_EVENT(kvm_fast_mmio,
  * Tracepoint for cpuid.
  */
 TRACE_EVENT(kvm_cpuid,
-	TP_PROTO(unsigned int function, unsigned long rax, unsigned long rbx,
-		 unsigned long rcx, unsigned long rdx, bool found),
-	TP_ARGS(function, rax, rbx, rcx, rdx, found),
+	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),
 
 	TP_STRUCT__entry(
 		__field(	unsigned int,	function	)
+		__field(	unsigned int,	index		)
 		__field(	unsigned long,	rax		)
 		__field(	unsigned long,	rbx		)
 		__field(	unsigned long,	rcx		)
@@ -166,15 +168,16 @@ TRACE_EVENT(kvm_cpuid,
 
 	TP_fast_assign(
 		__entry->function	= function;
+		__entry->index		= index;
 		__entry->rax		= rax;
 		__entry->rbx		= rbx;
 		__entry->rcx		= rcx;
 		__entry->rdx		= rdx;
 		__entry->found		= found;
 	),
 
-	TP_printk("func %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
-		  __entry->function, __entry->rax,
+	TP_printk("func %x idx %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
+		  __entry->function, __entry->index, __entry->rax,
 		  __entry->rbx, __entry->rcx, __entry->rdx,
 		  __entry->found ? "found" : "not found")
 );