[PATCH v2] drivers/xen: Improve the late XenStore init protocol

[Henry Wang <xin.wang2@xxxxxxx>]

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 <xin.wang2@xxxxxxx>
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
v2:
- Use -EINVAL for the memremap() check. (Stefano)
- Add Fixes: tag. (Stefano)
- Rework the condition for free_irq() in xenbus_probe(). (Stefano)
---
 drivers/xen/xenbus/xenbus_probe.c | 36 ++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c 
b/drivers/xen/xenbus/xenbus_probe.c
index 3205e5d724c8..1a9ded0cddcb 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -65,13 +65,17 @@
 #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);
 
@@ -751,19 +755,19 @@ static void xenbus_probe(void)
 {
        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
@@ -822,7 +826,7 @@ static int __init xenbus_probe_initcall(void)
        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();
 
        /*
@@ -831,7 +835,7 @@ static int __init xenbus_probe_initcall(void)
         * 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,
@@ -1014,6 +1018,12 @@ static int __init xenbus_init(void)
                        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;
                }
-- 
2.34.1