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    SubjectRe: [PATCH 2/6] arm64/vdso: Zap vvar pages when switching to a time namespace
    On Tue, Jun 16, 2020 at 12:55:41AM -0700, Andrei Vagin wrote:
    > 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.
    >
    > Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    > Reviewed-by: Dmitry Safonov <dima@arista.com>
    > Signed-off-by: Andrei Vagin <avagin@gmail.com>
    > ---
    > arch/arm64/kernel/vdso.c | 32 ++++++++++++++++++++++++++++++++
    > 1 file changed, 32 insertions(+)
    >
    > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
    > index b0aec4e8c9b4..df4bb736d28a 100644
    > --- a/arch/arm64/kernel/vdso.c
    > +++ b/arch/arm64/kernel/vdso.c
    > @@ -125,6 +125,38 @@ static int __vdso_init(enum vdso_abi abi)
    > return 0;
    > }
    >
    > +#ifdef CONFIG_TIME_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 re-faulted with a
    > + * corresponding layout.
    > + * See also the comment near timens_setup_vdso_data() for details.
    > + */
    > +int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
    > +{
    > + struct mm_struct *mm = task->mm;
    > + struct vm_area_struct *vma;
    > +
    > + if (mmap_write_lock_killable(mm))
    > + return -EINTR;

    Hey,

    Just a heads-up I'm about to plumb CLONE_NEWTIME support into setns()
    which would mean that vdso_join_timens() ould not be allowed to fail
    anymore to make it easy to switch to multiple namespaces atomically. So
    this would probably need to be changed to mmap_write_lock() which I've
    already brought up upstream:
    https://lore.kernel.org/lkml/20200611110221.pgd3r5qkjrjmfqa2@wittgenstein/
    (Assuming that people agree. I just sent the series and most people here
    are Cced.)

    Thanks!
    Christian

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