drivers/xen: Improve the late XenStore init protocol

Currently, the late XenStore init protocol is only triggered properly
for the case that HVM_PARAM_STORE_PFN is ~0ULL (invalid). For the
case that XenStore interface is allocated but not ready (the connection
status is not XENSTORE_CONNECTED), Linux should also wait until the
XenStore is set up properly.

Introduce a macro to describe the XenStore interface is ready, use
it in xenbus_probe_initcall() to select the code path of doing the
late XenStore init protocol or not. Since now we have more than one
condition for XenStore late init, rework the check in xenbus_probe()
for the free_irq().

Take the opportunity to enhance the check of the allocated XenStore
interface can be properly mapped, and return error early if the
memremap() fails.

Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain")
Signed-off-by: Henry Wang <[e-mail]>
Signed-off-by: Michal Orzel <[e-mail]>
Reviewed-by: Stefano Stabellini <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Juergen Gross <[e-mail]>

drivers/xen/xenbus/xenbus_probe.c

···
 #include "xenbus.h"
 
 
-static int xs_init_irq;
+static int xs_init_irq = -1;
 int xen_store_evtchn;
 EXPORT_SYMBOL_GPL(xen_store_evtchn);
 
 struct xenstore_domain_interface *xen_store_interface;
 EXPORT_SYMBOL_GPL(xen_store_interface);
+
+#define XS_INTERFACE_READY \
+	((xen_store_interface != NULL) && \
+	 (xen_store_interface->connection == XENSTORE_CONNECTED))
 
 enum xenstore_init xen_store_domain_type;
 EXPORT_SYMBOL_GPL(xen_store_domain_type);
···
 {
 	xenstored_ready = 1;
 
-	if (!xen_store_interface) {
+	if (!xen_store_interface)
 		xen_store_interface = memremap(xen_store_gfn << XEN_PAGE_SHIFT,
 					       XEN_PAGE_SIZE, MEMREMAP_WB);
-		/*
-		 * Now it is safe to free the IRQ used for xenstore late
-		 * initialization. No need to unbind: it is about to be
-		 * bound again from xb_init_comms. Note that calling
-		 * unbind_from_irqhandler now would result in xen_evtchn_close()
-		 * being called and the event channel not being enabled again
-		 * afterwards, resulting in missed event notifications.
-		 */
+	/*
+	 * Now it is safe to free the IRQ used for xenstore late
+	 * initialization. No need to unbind: it is about to be
+	 * bound again from xb_init_comms. Note that calling
+	 * unbind_from_irqhandler now would result in xen_evtchn_close()
+	 * being called and the event channel not being enabled again
+	 * afterwards, resulting in missed event notifications.
+	 */
+	if (xs_init_irq >= 0)
 		free_irq(xs_init_irq, &xb_waitq);
-	}
 
 	/*
 	 * In the HVM case, xenbus_init() deferred its call to
···
 	if (xen_store_domain_type == XS_PV ||
 	    (xen_store_domain_type == XS_HVM &&
 	     !xs_hvm_defer_init_for_callback() &&
-	     xen_store_interface != NULL))
+	     XS_INTERFACE_READY))
 		xenbus_probe();
 
 	/*
···
 	 * started, then probe.  It will be triggered when communication
 	 * starts happening, by waiting on xb_waitq.
 	 */
-	if (xen_store_domain_type == XS_LOCAL || xen_store_interface == NULL) {
+	if (xen_store_domain_type == XS_LOCAL || !XS_INTERFACE_READY) {
 		struct task_struct *probe_task;
 
 		probe_task = kthread_run(xenbus_probe_thread, NULL,
···
 			xen_store_interface =
 				memremap(xen_store_gfn << XEN_PAGE_SHIFT,
 					 XEN_PAGE_SIZE, MEMREMAP_WB);
+			if (!xen_store_interface) {
+				pr_err("%s: cannot map HVM_PARAM_STORE_PFN=%llx\n",
+				       __func__, v);
+				err = -EINVAL;
+				goto out_error;
+			}
 			if (xen_store_interface->connection != XENSTORE_CONNECTED)
 				wait = true;
 		}