[PATCHv4 02/28] timens: Add timens_offsets

[Dmitry Safonov]

From: Andrei Vagin <avagin@xxxxxxxxxx>

Introduce offsets for time namespace. They will contain an adjustment
needed to convert clocks to/from host's.

Allocate one page for each time namespace that will be premapped into
userspace among vvar pages.

Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Co-developed-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
 MAINTAINERS                    |  1 +
 include/linux/time_namespace.h |  1 +
 include/linux/timens_offsets.h |  8 ++++++++
 kernel/time_namespace.c        | 14 ++++++++++++--
 4 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/timens_offsets.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 323ab92b963b..bf55aec42f2d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12590,6 +12590,7 @@ S:	Maintained
 F:	fs/timerfd.c
 F:	include/linux/timer*
 F:	include/linux/time_namespace.h
+F:	include/linux/timens_offsets.h
 F:	kernel/time_namespace.c
 F:	kernel/time/*timer*
 
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 9507ed7072fe..b6985aa87479 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -8,6 +8,7 @@
 #include <linux/nsproxy.h>
 #include <linux/ns_common.h>
 #include <linux/err.h>
+#include <linux/timens_offsets.h>
 
 struct user_namespace;
 extern struct user_namespace init_user_ns;
diff --git a/include/linux/timens_offsets.h b/include/linux/timens_offsets.h
new file mode 100644
index 000000000000..7d7cb68ea778
--- /dev/null
+++ b/include/linux/timens_offsets.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_TIME_OFFSETS_H
+#define _LINUX_TIME_OFFSETS_H
+
+struct timens_offsets {
+};
+
+#endif
diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
index 8c600df9771d..4828447721ec 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c
@@ -13,6 +13,7 @@
 #include <linux/user_namespace.h>
 #include <linux/proc_ns.h>
 #include <linux/sched/task.h>
+#include <linux/mm.h>
 
 static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
 {
@@ -46,6 +47,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 {
 	struct time_namespace *ns;
 	struct ucounts *ucounts;
+	struct page *page;
 	int err;
 
 	err = -ENOSPC;
@@ -58,15 +60,22 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 	if (!ns)
 		goto fail_dec;
 
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page)
+		goto fail_free;
+	ns->offsets = page_address(page);
+	BUILD_BUG_ON(sizeof(*ns->offsets) > PAGE_SIZE);
+
 	err = ns_alloc_inum(&ns->ns);
 	if (err)
-		goto fail_free;
+		goto fail_page;
 
 	ns->ucounts = ucounts;
 	ns->ns.ops = &timens_operations;
 	ns->user_ns = get_user_ns(user_ns);
 	return ns;
-
+fail_page:
+	free_page((unsigned long)ns->offsets);
 fail_free:
 	kfree(ns);
 fail_dec:
@@ -94,6 +103,7 @@ void free_time_ns(struct kref *kref)
 	struct time_namespace *ns;
 
 	ns = container_of(kref, struct time_namespace, kref);
+	free_page((unsigned long)ns->offsets);
 	dec_time_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
-- 
2.22.0