hw/xen: detect when running inside stubdomain

Introduce global xen_is_stubdomain variable when qemu is running inside
a stubdomain instead of dom0. This will be relevant for subsequent
patches, as few things like accessing PCI config space need to be done
differently.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <e66aa97dca5120f22e015c19710b2ff04f525720.1711506237.git-series.marmarek@invisiblethingslab.com>
Signed-off-by: Anthony PERARD <anthony@xenproject.org>

hw/i386/xen/xen-hvm.c

@@ -584,6 +584,26 @@ static void xen_wakeup_notifier(Notifier *notifier, void *data)
     xc_set_hvm_param(xen_xc, xen_domid, HVM_PARAM_ACPI_S_STATE, 0);
 }
 
+static bool xen_check_stubdomain(struct xs_handle *xsh)
+{
+    char *dm_path = g_strdup_printf(
+        "/local/domain/%d/image/device-model-domid", xen_domid);
+    char *val;
+    int32_t dm_domid;
+    bool is_stubdom = false;
+
+    val = xs_read(xsh, 0, dm_path, NULL);
+    if (val) {
+        if (sscanf(val, "%d", &dm_domid) == 1) {
+            is_stubdom = dm_domid != 0;
+        }
+        free(val);
+    }
+
+    g_free(dm_path);
+    return is_stubdom;
+}
+
 void xen_hvm_init_pc(PCMachineState *pcms, MemoryRegion **ram_memory)
 {
     MachineState *ms = MACHINE(pcms);
@@ -596,6 +616,8 @@ void xen_hvm_init_pc(PCMachineState *pcms, MemoryRegion **ram_memory)
 
     xen_register_ioreq(state, max_cpus, &xen_memory_listener);
 
+    xen_is_stubdomain = xen_check_stubdomain(state->xenstore);
+
     QLIST_INIT(&xen_physmap);
     xen_read_physmap(state);
 

include/hw/xen/xen.h

@@ -36,6 +36,7 @@ enum xen_mode {
 extern uint32_t xen_domid;
 extern enum xen_mode xen_mode;
 extern bool xen_domid_restrict;
+extern bool xen_is_stubdomain;
 
 int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num);
 int xen_set_pci_link_route(uint8_t link, uint8_t irq);

system/globals.c

@@ -60,6 +60,7 @@ bool qemu_uuid_set;
 uint32_t xen_domid;
 enum xen_mode xen_mode = XEN_DISABLED;
 bool xen_domid_restrict;
+bool xen_is_stubdomain;
 struct evtchn_backend_ops *xen_evtchn_ops;
 struct gnttab_backend_ops *xen_gnttab_ops;
 struct foreignmem_backend_ops *xen_foreignmem_ops;