vdso/timens: Move functions to new file

As a preparation of the untangling of time namespaces and the vDSO, move
the glue functions between those subsystems into a new file.

While at it, switch the mutex lock and mmap_read_lock() in the vDSO
namespace code to guard().

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260326-vdso-timens-decoupling-v2-1-c82693a7775f@linutronix.de

4 files changed, 164 insertions, 121 deletions

diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index f7d52d9543cc..662bccb3b7f9 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -29,6 +29,6 @@ endif
 obj-$(CONFIG_GENERIC_GETTIMEOFDAY)		+= vsyscall.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
-obj-$(CONFIG_TIME_NS)				+= namespace.o
+obj-$(CONFIG_TIME_NS)				+= namespace.o namespace_vdso.o
 obj-$(CONFIG_TEST_CLOCKSOURCE_WATCHDOG)		+= clocksource-wdtest.o
 obj-$(CONFIG_TIME_KUNIT_TEST)			+= time_test.o
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 652744e00eb4..903f55a2dfb2 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -19,7 +19,7 @@
 #include <linux/err.h>
 #include <linux/mm.h>
 
-#include <vdso/datapage.h>
+#include "namespace_internal.h"
 
 ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
 				struct timens_offsets *ns_offsets)
@@ -138,117 +138,7 @@ struct time_namespace *copy_time_ns(u64 flags,
 	return clone_time_ns(user_ns, old_ns);
 }
 
-static struct timens_offset offset_from_ts(struct timespec64 off)
-{
-	struct timens_offset ret;
-
-	ret.sec = off.tv_sec;
-	ret.nsec = off.tv_nsec;
-
-	return ret;
-}
-
-/*
- * A time namespace VVAR page has the same layout as the VVAR page which
- * contains the system wide VDSO data.
- *
- * For a normal task the VVAR pages are installed in the normal ordering:
- *     VVAR
- *     PVCLOCK
- *     HVCLOCK
- *     TIMENS   <- Not really required
- *
- * Now for a timens task the pages are installed in the following order:
- *     TIMENS
- *     PVCLOCK
- *     HVCLOCK
- *     VVAR
- *
- * The check for vdso_clock->clock_mode is in the unlikely path of
- * the seq begin magic. So for the non-timens case most of the time
- * 'seq' is even, so the branch is not taken.
- *
- * If 'seq' is odd, i.e. a concurrent update is in progress, the extra check
- * for vdso_clock->clock_mode is a non-issue. The task is spin waiting for the
- * update to finish and for 'seq' to become even anyway.
- *
- * Timens page has vdso_clock->clock_mode set to VDSO_CLOCKMODE_TIMENS which
- * enforces the time namespace handling path.
- */
-static void timens_setup_vdso_clock_data(struct vdso_clock *vc,
-					 struct time_namespace *ns)
-{
-	struct timens_offset *offset = vc->offset;
-	struct timens_offset monotonic = offset_from_ts(ns->offsets.monotonic);
-	struct timens_offset boottime = offset_from_ts(ns->offsets.boottime);
-
-	vc->seq				= 1;
-	vc->clock_mode			= VDSO_CLOCKMODE_TIMENS;
-	offset[CLOCK_MONOTONIC]		= monotonic;
-	offset[CLOCK_MONOTONIC_RAW]	= monotonic;
-	offset[CLOCK_MONOTONIC_COARSE]	= monotonic;
-	offset[CLOCK_BOOTTIME]		= boottime;
-	offset[CLOCK_BOOTTIME_ALARM]	= boottime;
-}
-
-struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops().
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-
-/*
- * Protects possibly multiple offsets writers racing each other
- * and tasks entering the namespace.
- */
-static DEFINE_MUTEX(offset_lock);
-
-static void timens_set_vvar_page(struct task_struct *task,
-				struct time_namespace *ns)
-{
-	struct vdso_time_data *vdata;
-	struct vdso_clock *vc;
-	unsigned int i;
-
-	if (ns == &init_time_ns)
-		return;
-
-	/* Fast-path, taken by every task in namespace except the first. */
-	if (likely(ns->frozen_offsets))
-		return;
-
-	mutex_lock(&offset_lock);
-	/* Nothing to-do: vvar_page has been already initialized. */
-	if (ns->frozen_offsets)
-		goto out;
-
-	ns->frozen_offsets = true;
-	vdata = page_address(ns->vvar_page);
-	vc = vdata->clock_data;
-
-	for (i = 0; i < CS_BASES; i++)
-		timens_setup_vdso_clock_data(&vc[i], ns);
-
-	if (IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS)) {
-		for (i = 0; i < ARRAY_SIZE(vdata->aux_clock_data); i++)
-			timens_setup_vdso_clock_data(&vdata->aux_clock_data[i], ns);
-	}
-
-out:
-	mutex_unlock(&offset_lock);
-}
+DEFINE_MUTEX(timens_offset_lock);
 
 void free_time_ns(struct time_namespace *ns)
 {
@@ -298,12 +188,6 @@ static void timens_put(struct ns_common *ns)
 	put_time_ns(to_time_ns(ns));
 }
 
-void timens_commit(struct task_struct *tsk, struct time_namespace *ns)
-{
-	timens_set_vvar_page(tsk, ns);
-	vdso_join_timens(tsk, ns);
-}
-
 static int timens_install(struct nsset *nsset, struct ns_common *new)
 {
 	struct nsproxy *nsproxy = nsset->nsproxy;
@@ -428,7 +312,7 @@ int proc_timens_set_offset(struct file *file, struct task_struct *p,
 			goto out;
 	}
 
-	mutex_lock(&offset_lock);
+	mutex_lock(&timens_offset_lock);
 	if (time_ns->frozen_offsets) {
 		err = -EACCES;
 		goto out_unlock;
@@ -453,7 +337,7 @@ int proc_timens_set_offset(struct file *file, struct task_struct *p,
 	}
 
 out_unlock:
-	mutex_unlock(&offset_lock);
+	mutex_unlock(&timens_offset_lock);
 out:
 	put_time_ns(time_ns);
 
diff --git a/kernel/time/namespace_internal.h b/kernel/time/namespace_internal.h
new file mode 100644
index 000000000000..e85da11abb4d
--- /dev/null
+++ b/kernel/time/namespace_internal.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TIME_NAMESPACE_INTERNAL_H
+#define _TIME_NAMESPACE_INTERNAL_H
+
+#include <linux/mutex.h>
+
+/*
+ * Protects possibly multiple offsets writers racing each other
+ * and tasks entering the namespace.
+ */
+extern struct mutex timens_offset_lock;
+
+#endif /* _TIME_NAMESPACE_INTERNAL_H */
diff --git a/kernel/time/namespace_vdso.c b/kernel/time/namespace_vdso.c
new file mode 100644
index 000000000000..0e154f901501
--- /dev/null
+++ b/kernel/time/namespace_vdso.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Author: Andrei Vagin <avagin@openvz.org>
+ * Author: Dmitry Safonov <dima@arista.com>
+ */
+
+#include <linux/cleanup.h>
+#include <linux/mm.h>
+#include <linux/time_namespace.h>
+#include <linux/time.h>
+#include <linux/vdso_datastore.h>
+
+#include <vdso/clocksource.h>
+#include <vdso/datapage.h>
+
+#include "namespace_internal.h"
+
+static struct timens_offset offset_from_ts(struct timespec64 off)
+{
+	struct timens_offset ret;
+
+	ret.sec = off.tv_sec;
+	ret.nsec = off.tv_nsec;
+
+	return ret;
+}
+
+/*
+ * A time namespace VVAR page has the same layout as the VVAR page which
+ * contains the system wide VDSO data.
+ *
+ * For a normal task the VVAR pages are installed in the normal ordering:
+ *     VVAR
+ *     PVCLOCK
+ *     HVCLOCK
+ *     TIMENS   <- Not really required
+ *
+ * Now for a timens task the pages are installed in the following order:
+ *     TIMENS
+ *     PVCLOCK
+ *     HVCLOCK
+ *     VVAR
+ *
+ * The check for vdso_clock->clock_mode is in the unlikely path of
+ * the seq begin magic. So for the non-timens case most of the time
+ * 'seq' is even, so the branch is not taken.
+ *
+ * If 'seq' is odd, i.e. a concurrent update is in progress, the extra check
+ * for vdso_clock->clock_mode is a non-issue. The task is spin waiting for the
+ * update to finish and for 'seq' to become even anyway.
+ *
+ * Timens page has vdso_clock->clock_mode set to VDSO_CLOCKMODE_TIMENS which
+ * enforces the time namespace handling path.
+ */
+static void timens_setup_vdso_clock_data(struct vdso_clock *vc,
+					 struct time_namespace *ns)
+{
+	struct timens_offset *offset = vc->offset;
+	struct timens_offset monotonic = offset_from_ts(ns->offsets.monotonic);
+	struct timens_offset boottime = offset_from_ts(ns->offsets.boottime);
+
+	vc->seq				= 1;
+	vc->clock_mode			= VDSO_CLOCKMODE_TIMENS;
+	offset[CLOCK_MONOTONIC]		= monotonic;
+	offset[CLOCK_MONOTONIC_RAW]	= monotonic;
+	offset[CLOCK_MONOTONIC_COARSE]	= monotonic;
+	offset[CLOCK_BOOTTIME]		= boottime;
+	offset[CLOCK_BOOTTIME_ALARM]	= boottime;
+}
+
+struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_mm == current->mm))
+		return current->nsproxy->time_ns->vvar_page;
+
+	/*
+	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
+	 * through interfaces like /proc/$pid/mem or
+	 * process_vm_{readv,writev}() as long as there's no .access()
+	 * in special_mapping_vmops().
+	 * For more details check_vma_flags() and __access_remote_vm()
+	 */
+
+	WARN(1, "vvar_page accessed remotely");
+
+	return NULL;
+}
+
+static void timens_set_vvar_page(struct task_struct *task,
+				struct time_namespace *ns)
+{
+	struct vdso_time_data *vdata;
+	struct vdso_clock *vc;
+	unsigned int i;
+
+	if (ns == &init_time_ns)
+		return;
+
+	/* Fast-path, taken by every task in namespace except the first. */
+	if (likely(ns->frozen_offsets))
+		return;
+
+	guard(mutex)(&timens_offset_lock);
+	/* Nothing to-do: vvar_page has been already initialized. */
+	if (ns->frozen_offsets)
+		return;
+
+	ns->frozen_offsets = true;
+	vdata = page_address(ns->vvar_page);
+	vc = vdata->clock_data;
+
+	for (i = 0; i < CS_BASES; i++)
+		timens_setup_vdso_clock_data(&vc[i], ns);
+
+	if (IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS)) {
+		for (i = 0; i < ARRAY_SIZE(vdata->aux_clock_data); i++)
+			timens_setup_vdso_clock_data(&vdata->aux_clock_data[i], ns);
+	}
+}
+
+/*
+ * The vvar page layout depends on whether a task belongs to the root or
+ * non-root time namespace. Whenever a task changes its namespace, the VVAR
+ * page tables are cleared and then they will be re-faulted with a
+ * corresponding layout.
+ * See also the comment near timens_setup_vdso_clock_data() for details.
+ */
+static int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
+{
+	struct mm_struct *mm = task->mm;
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	guard(mmap_read_lock)(mm);
+	for_each_vma(vmi, vma) {
+		if (vma_is_special_mapping(vma, &vdso_vvar_mapping))
+			zap_vma_pages(vma);
+	}
+	return 0;
+}
+
+void timens_commit(struct task_struct *tsk, struct time_namespace *ns)
+{
+	timens_set_vvar_page(tsk, ns);
+	vdso_join_timens(tsk, ns);
+}