[PATCHv6 02/36] timens: Add timens_offsets

[Dmitry Safonov <dima@arista.com>]

From: Andrei Vagin <avagin@openvz.org>

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.

A new namespace is created with the same offsets as the time namespace
of the current process.

Signed-off-by: Andrei Vagin <avagin@openvz.org>
Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 MAINTAINERS                    |  1 +
 include/linux/time_namespace.h | 18 ++++++++++++++++++
 include/linux/timens_offsets.h | 10 ++++++++++
 kernel/time_namespace.c        | 16 ++++++++++++++--
 4 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/timens_offsets.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 97b7737f5aba..527aee1e616f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12899,6 +12899,7 @@ 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..334c1a1c6607 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;
@@ -39,6 +40,21 @@ static inline void put_time_ns(struct time_namespace *ns)
 	kref_put(&ns->kref, free_time_ns);
 }
 
+static inline void timens_add_monotonic(struct timespec64 *ts)
+{
+	struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
+
+	if (ns_offsets)
+		*ts = timespec64_add(*ts, ns_offsets->monotonic);
+}
+
+static inline void timens_add_boottime(struct timespec64 *ts)
+{
+	struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
+
+	if (ns_offsets)
+		*ts = timespec64_add(*ts, ns_offsets->boottime);
+}
 
 #else
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
@@ -64,6 +80,8 @@ static inline int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *ts
 	return 0;
 }
 
+static inline void timens_add_monotonic(struct timespec64 *ts) {}
+static inline void timens_add_boottime(struct timespec64 *ts) {}
 #endif
 
 #endif /* _LINUX_TIMENS_H */
diff --git a/include/linux/timens_offsets.h b/include/linux/timens_offsets.h
new file mode 100644
index 000000000000..e93aabaa5e45
--- /dev/null
+++ b/include/linux/timens_offsets.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_TIME_OFFSETS_H
+#define _LINUX_TIME_OFFSETS_H
+
+struct timens_offsets {
+	struct timespec64 monotonic;
+	struct timespec64 boottime;
+};
+
+#endif
diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
index 8fd8384b7261..394a9e168e7c 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/err.h>
+#include <linux/mm.h>
 
 static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
 {
@@ -47,6 +48,7 @@ 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;
@@ -59,15 +61,24 @@ 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);
+	if (old_ns->offsets)
+		memcpy(ns->offsets, old_ns->offsets, sizeof(struct timens_offsets));
+	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:
@@ -95,6 +106,7 @@ 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