xen: fix build without pci passthrough

Xen PCI passthrough support may not be available and thus the global
variable "has_igd_gfx_passthru" might be compiled out. Common code
should not access it in that case.

Unfortunately, we can't use CONFIG_XEN_PCI_PASSTHROUGH directly in
xen-common.c so this patch instead move access to the
has_igd_gfx_passthru variable via function and those functions are
also implemented as stubs. The stubs will be used when QEMU is built
without passthrough support.

Now, when one will want to enable igd-passthru via the -machine
property, they will get an error message if QEMU is built without
passthrough support.

Fixes: 46472d8232 ('xen: convert "-machine igd-passthru" to an accelerator property')
Reported-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20200603160442.3151170-1-anthony.perard@citrix.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/xen/xen-all.c

@@ -137,12 +137,12 @@ static void xen_change_state_handler(void *opaque, int running,
 
 static bool xen_get_igd_gfx_passthru(Object *obj, Error **errp)
 {
-    return has_igd_gfx_passthru;
+    return xen_igd_gfx_pt_enabled();
 }
 
 static void xen_set_igd_gfx_passthru(Object *obj, bool value, Error **errp)
 {
-    has_igd_gfx_passthru = value;
+    xen_igd_gfx_pt_set(value, errp);
 }
 
 static void xen_setup_post(MachineState *ms, AccelState *accel)

hw/Makefile.objs

@@ -35,7 +35,7 @@ devices-dirs-y += usb/
 devices-dirs-$(CONFIG_VFIO) += vfio/
 devices-dirs-y += virtio/
 devices-dirs-y += watchdog/
-devices-dirs-y += xen/
+devices-dirs-$(CONFIG_XEN) += xen/
 devices-dirs-$(CONFIG_MEM_DEVICE) += mem/
 devices-dirs-$(CONFIG_NUBUS) += nubus/
 devices-dirs-y += semihosting/

hw/i386/pc_piix.c

@@ -377,7 +377,7 @@ static void pc_init_isa(MachineState *machine)
 #ifdef CONFIG_XEN
 static void pc_xen_hvm_init_pci(MachineState *machine)
 {
-    const char *pci_type = has_igd_gfx_passthru ?
+    const char *pci_type = xen_igd_gfx_pt_enabled() ?
                 TYPE_IGD_PASSTHROUGH_I440FX_PCI_DEVICE : TYPE_I440FX_PCI_DEVICE;
 
     pc_init1(machine,

hw/xen/Makefile.objs

@@ -1,6 +1,7 @@
 # xen backend driver support
-common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-bus.o xen-bus-helper.o xen-backend.o
+common-obj-y += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-bus.o xen-bus-helper.o xen-backend.o
 
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o xen_pt_graphics.o xen_pt_msi.o
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt_load_rom.o
+obj-$(call $(lnot, $(CONFIG_XEN_PCI_PASSTHROUGH))) += xen_pt_stub.o

hw/xen/xen_pt.c

@@ -65,7 +65,17 @@
 #include "qemu/range.h"
 #include "exec/address-spaces.h"
 
-bool has_igd_gfx_passthru;
+static bool has_igd_gfx_passthru;
+
+bool xen_igd_gfx_pt_enabled(void)
+{
+    return has_igd_gfx_passthru;
+}
+
+void xen_igd_gfx_pt_set(bool value, Error **errp)
+{
+    has_igd_gfx_passthru = value;
+}
 
 #define XEN_PT_NR_IRQS (256)
 static uint8_t xen_pt_mapped_machine_irq[XEN_PT_NR_IRQS] = {0};

hw/xen/xen_pt.h

@@ -5,6 +5,9 @@
 #include "hw/pci/pci.h"
 #include "xen-host-pci-device.h"
 
+bool xen_igd_gfx_pt_enabled(void);
+void xen_igd_gfx_pt_set(bool value, Error **errp);
+
 void xen_pt_log(const PCIDevice *d, const char *f, ...) GCC_FMT_ATTR(2, 3);
 
 #define XEN_PT_ERR(d, _f, _a...) xen_pt_log(d, "%s: Error: "_f, __func__, ##_a)
@@ -322,10 +325,9 @@ extern void *pci_assign_dev_load_option_rom(PCIDevice *dev,
                                             unsigned int domain,
                                             unsigned int bus, unsigned int slot,
                                             unsigned int function);
-extern bool has_igd_gfx_passthru;
 static inline bool is_igd_vga_passthrough(XenHostPCIDevice *dev)
 {
-    return (has_igd_gfx_passthru
+    return (xen_igd_gfx_pt_enabled()
             && ((dev->class_code >> 0x8) == PCI_CLASS_DISPLAY_VGA));
 }
 int xen_pt_register_vga_regions(XenHostPCIDevice *dev);

hw/xen/xen_pt_stub.c

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2020       Citrix Systems UK Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "hw/xen/xen_pt.h"
+#include "qapi/error.h"
+
+bool xen_igd_gfx_pt_enabled(void)
+{
+    return false;
+}
+
+void xen_igd_gfx_pt_set(bool value, Error **errp)
+{
+    if (value) {
+        error_setg(errp, "Xen PCI passthrough support not built in");
+    }
+}