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

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Date: Wed, 15 May 2024 09:43:30 +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] 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() and xenbus_probe() to select the code
path of doing the late XenStore init protocol or not.

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

Signed-off-by: Henry Wang <xin.wang2@....com>
Signed-off-by: Michal Orzel <michal.orzel@....com>
---
 drivers/xen/xenbus/xenbus_probe.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 3205e5d724c8..8aec0ed1d047 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -72,6 +72,10 @@ 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);
 
@@ -751,9 +755,10 @@ static void xenbus_probe(void)
 {
 	xenstored_ready = 1;
 
-	if (!xen_store_interface) {
-		xen_store_interface = memremap(xen_store_gfn << XEN_PAGE_SHIFT,
-					       XEN_PAGE_SIZE, MEMREMAP_WB);
+	if (!xen_store_interface || XS_INTERFACE_READY) {
+		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
@@ -822,7 +827,7 @@ 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 +836,7 @@ 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 +1019,12 @@ 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 = -ENOMEM;
+				goto out_error;
+			}
 			if (xen_store_interface->connection != XENSTORE_CONNECTED)
 				wait = true;
 		}
-- 
2.34.1