• Goran Ferenc's avatar
    MIPS: VDSO: Fix conversions in do_monotonic()/do_monotonic_coarse() · 8ec7f15b
    Goran Ferenc authored
    Fix incorrect calculation in do_monotonic() and do_monotonic_coarse()
    function that in turn caused incorrect values returned by the vdso
    version of system call clock_gettime() on mips64 if its system clock
    Consider these variables and their types on mips32 and mips64:
    tk->wall_to_monotonic.tv_sec  s64, s64   (kernel/vdso.c)
    vdso_data.wall_to_mono_sec    u32, u32   (kernel/vdso.c)
    to_mono_sec                   u32, u32   (vdso/gettimeofday.c)
    ts->tv_sec                    s32, s64   (vdso/gettimeofday.c)
    For mips64 case, u32 vdso_data.wall_to_mono_sec variable is updated
    from the 64-bit signed variable tk->wall_to_monotonic.tv_sec
    (kernel/vdso.c:76) which is a negative number holding the time passed
    from 1970-01-01 to the time boot started. This 64-bit signed value is
    currently around 47+ years, in seconds. For instance, let this value
    11111111111111111111111111111111 10100111001101000001101011101011
    By updating 32-bit vdso_data.wall_to_mono_sec variable, we lose upper
    32 bits (signed 1's).
    to_mono_sec variable is a parameter of do_monotonic() and
    do_monotonic_coarse() functions which holds vdso_data.wall_to_mono_sec
    value. Its value needs to be added (or subtracted considering it holds
    negative value from the tk->wall_to_monotonic.tv_sec) to the current
    time passed from 1970-01-01 (ts->tv_sec), which is again something like
    47+ years, but increased by the time passed from the boot to the
    current time. ts->tv_sec is 32-bit long in case of 32-bit architecture
    and 64-bit long in case of 64-bit architecture. Consider the update of
    ts->tv_sec (vdso/gettimeofday.c:55 & 167):
    ts->tv_sec += to_mono_sec;
    mips32 case: This update will be performed correctly, since both
    ts->tv_sec and to_mono_sec are 32-bit long and the sign in to_mono_sec
    is preserved. Implicit conversion from u32 to s32 will be done
    mips64 case: This update will be wrong, since the implicit conversion
    will not be done correctly. The reason is that the conversion will be
    from u32 to s64. This is because to_mono_sec is 32-bit long for both
    mips32 and mips64 cases and s64..33 bits of converted to_mono_sec
    variable will be zeros.
    So, in order to make MIPS64 implementation work properly for
    MONOTONIC and MONOTONIC_COARSE clock ids on mips64, the size of
    wall_to_mono_sec variable in mips_vdso_data union and respective
    parameters in do_monotonic() and do_monotonic_coarse() functions
    should be changed from u32 to u64. Because of consistency, this
    size change from u32 and u64 is also done for wall_to_mono_nsec
    variable and corresponding function parameters.
    As far as similar situations for other architectures are concerned,
    let's take a look at arm. Arm has two distinct vdso_data structures
    for 32-bit & 64-bit cases, and arm's wall_to_mono_sec and
    wall_to_mono_nsec are u32 for 32-bit and u64 for 64-bit cases.
    On the other hand, MIPS has only one structure (mips_vdso_data),
    hence the need for changing the size of above mentioned parameters.
    Signed-off-by: default avatarGoran Ferenc <goran.ferenc@imgtec.com>
    Signed-off-by: default avatarMiodrag Dinic <miodrag.dinic@imgtec.com>
    Signed-off-by: default avatarAleksandar Markovic <aleksandar.markovic@imgtec.com>
    Cc: Douglas Leung <douglas.leung@imgtec.com>
    Cc: James Hogan <james.hogan@imgtec.com>
    Cc: Paul Burton <paul.burton@imgtec.com>
    Cc: Petar Jovanovic <petar.jovanovic@imgtec.com>
    Cc: Raghu Gandham <raghu.gandham@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Cc: linux-kernel@vger.kernel.org
    Patchwork: https://patchwork.linux-mips.org/patch/16638/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
vdso.h 3.73 KB