Re: [PATCH 2/6] arm64/vdso: Zap vvar pages when switching to a time namespace

From: Andrei Vagin
Date: Thu Jun 25 2020 - 04:25:50 EST


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:
> > 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@xxxxxxx>
> > Reviewed-by: Dmitry Safonov <dima@xxxxxxxxxx>
> > Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
> > ---
> > 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 <christian.brauner@xxxxxxxxxx>
>
> Thanks!
> Christian