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

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Date: Fri, 17 May 2024 09:15:16 +0800
From: Henry Wang <xin.wang2@....com>
To: <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
CC: Henry Wang <xin.wang2@....com>, Juergen Gross <jgross@...e.com>, "Stefano
 Stabellini" <sstabellini@...nel.org>, Oleksandr Tyshchenko
	<oleksandr_tyshchenko@...m.com>, Michal Orzel <michal.orzel@....com>
Subject: [PATCH v2] 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 <xin.wang2@....com>
Signed-off-by: Michal Orzel <michal.orzel@....com>
---
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