On Wed, Jun 24, 2020 at 05:18:01PM +0200, Christian Brauner wrote:

On Wed, Jun 24, 2020 at 01:33:17AM -0700, Andrei Vagin wrote:

quoted

The order of vvar pages depends on whether a task belongs to the root
time namespace or not. In the root time namespace, a task doesn't have a
per-namespace page. In a non-root namespace, the VVAR page which contains
the system-wide VDSO data is replaced with a namespace specific page
that contains clock offsets.

Whenever a task changes its namespace, the VVAR page tables are cleared
and then they will be re-faulted with a corresponding layout.

A task can switch its time namespace only if its ->mm isn't shared with
another task.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Dmitry Safonov <redacted>
Signed-off-by: Andrei Vagin <redacted>
---
 arch/arm64/kernel/vdso.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 7c4620451fa5..bdf492a17dff 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c

@@ -124,6 +124,37 @@ static int __vdso_init(enum vdso_abi abi)
 	return 0;
 }
 
+#ifdef CONFIG_TIME_NS
+/*
+ * The vvar mapping contains data for a specific time namespace, so when a task
+ * changes namespace we must unmap its vvar data for the old namespace.
+ * Subsequent faults will map in data for the new namespace.
+ *
+ * For more details see timens_setup_vdso_data().
+ */
+int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
+{
+	struct mm_struct *mm = task->mm;
+	struct vm_area_struct *vma;
+
+	mmap_read_lock(mm);

Perfect, thanks! I'll adapt my patches so that my change and this change
don't conflict and can go in together. Once they're landed we can simply
turn int vdso_join_timens() into void vdso_join_timens() everywhere.

Yep. Let's do it this way. Thanks!

Reviewed-by: Christian Brauner <redacted>

Thanks!
Christian

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