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    SubjectRe: [PATCH v5 0/6] arm64: add the time namespace support
    On Wed, Jun 24, 2020 at 01:33:15AM -0700, Andrei Vagin wrote:
    > Allocate the time namespace page among VVAR pages and add the logic
    > to handle faults on VVAR properly.
    >
    > If a task belongs to a time namespace then the VVAR page which contains
    > the system wide VDSO data is replaced with a namespace specific page
    > which has the same layout as the VVAR page. That page has vdso_data->seq
    > set to 1 to enforce the slow path and vdso_data->clock_mode set to
    > VCLOCK_TIMENS to enforce the time namespace handling path.
    >
    > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
    > update of the VDSO data is in progress, is not really affecting regular
    > tasks which are not part of a time namespace as the task is spin waiting
    > for the update to finish and vdso_data->seq to become even again.
    >
    > If a time namespace task hits that code path, it invokes the corresponding
    > time getter function which retrieves the real VVAR page, reads host time
    > and then adds the offset for the requested clock which is stored in the
    > special VVAR page.
    >

    > v2: Code cleanups suggested by Vincenzo.
    > v3: add a comment in __arch_get_timens_vdso_data.
    > v4: - fix an issue reported by the lkp robot.
    > - vvar has the same size with/without CONFIG_TIME_NAMESPACE, but the
    > timens page isn't allocated on !CONFIG_TIME_NAMESPACE. This
    > simplifies criu/vdso migration between different kernel configs.
    > v5: - Code cleanups suggested by Mark Rutland.
    > - In vdso_join_timens, mmap_write_lock is downgraded to
    > mmap_read_lock. The VMA list isn't changed there, zap_page_range
    > doesn't require mmap_write_lock.
    >
    > Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    > Reviewed-by: Dmitry Safonov <dima@arista.com>

    Hello Will and Catalin,

    Have you had a chance to look at this patch set? I think it is ready to be
    merged. Let me know if you have any questions.

    Thanks,
    Andrei

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