• Andrei Vagin's avatar
    arm64/vdso: Add time namespace page · 3503d56c
    Andrei Vagin authored
    Allocate the time namespace page among VVAR pages.  Provide
    __arch_get_timens_vdso_data() helper for VDSO code to get the
    code-relative position of VVARs on that special page.
    
    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.
    
    The time-namespace page isn't allocated on !CONFIG_TIME_NAMESPACE, but
    vma is the same size, which simplifies criu/vdso migration between
    different kernel configs.
    Signed-off-by: default avatarAndrei Vagin <avagin@gmail.com>
    Reviewed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
    Reviewed-by: default avatarDmitry Safonov <dima@arista.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Link: https://lore.kernel.org/r/20200624083321.144975-4-avagin@gmail.comSigned-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    3503d56c
compat_gettimeofday.h 4.04 KB