KVM: x86: move all vcpu->arch.pio* setup in emulator_pio_in_out()

For now, this is basically an excuse to add back the void* argument to
the function, while removing some knowledge of vcpu->arch.pio* from
its callers.  The WARN that vcpu->arch.pio.count is zero is also
extended to OUT operations.

The vcpu->arch.pio* fields still need to be filled even when the PIO is
handled in-kernel as __emulator_pio_in() is always followed by
complete_emulator_pio_in().  But after fixing that, it will be possible to
to only populate the vcpu->arch.pio* fields on userspace exits.

No functional change intended.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/trace.h

@@ -154,7 +154,7 @@ TRACE_EVENT(kvm_xen_hypercall,
 
 TRACE_EVENT(kvm_pio,
 	TP_PROTO(unsigned int rw, unsigned int port, unsigned int size,
-		 unsigned int count, void *data),
+		 unsigned int count, const void *data),
 	TP_ARGS(rw, port, size, count, data),
 
 	TP_STRUCT__entry(

arch/x86/kvm/x86.c

@@ -7576,17 +7576,25 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 }
 
 static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
-			       unsigned short port,
+			       unsigned short port, void *data,
 			       unsigned int count, bool in)
 {
-	void *data = vcpu->arch.pio_data;
 	unsigned i;
 	int r;
 
+	WARN_ON_ONCE(vcpu->arch.pio.count);
 	vcpu->arch.pio.port = port;
 	vcpu->arch.pio.in = in;
 	vcpu->arch.pio.count = count;
 	vcpu->arch.pio.size = size;
+	if (in) {
+		/* The buffer is only used in complete_emulator_pio_in().  */
+		WARN_ON(data);
+		memset(vcpu->arch.pio_data, 0, size * count);
+	} else {
+		memcpy(vcpu->arch.pio_data, data, size * count);
+	}
+	data = vcpu->arch.pio_data;
 
 	for (i = 0; i < count; i++) {
 		if (in)
@@ -7623,9 +7631,7 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
 static int __emulator_pio_in(struct kvm_vcpu *vcpu, int size,
 			     unsigned short port, unsigned int count)
 {
-	WARN_ON(vcpu->arch.pio.count);
-	memset(vcpu->arch.pio_data, 0, size * count);
-	return emulator_pio_in_out(vcpu, size, port, count, true);
+	return emulator_pio_in_out(vcpu, size, port, NULL, count, true);
 }
 
 static void complete_emulator_pio_in(struct kvm_vcpu *vcpu, void *val)
@@ -7674,9 +7680,8 @@ static int emulator_pio_out(struct kvm_vcpu *vcpu, int size,
 {
 	int ret;
 
-	memcpy(vcpu->arch.pio_data, val, size * count);
-	trace_kvm_pio(KVM_PIO_OUT, port, size, count, vcpu->arch.pio_data);
-	ret = emulator_pio_in_out(vcpu, size, port, count, false);
+	trace_kvm_pio(KVM_PIO_OUT, port, size, count, val);
+	ret = emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
 	if (ret)
                 vcpu->arch.pio.count = 0;