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    Subject[PATCH 5.1 190/405] arm64: vdso: Fix clock_getres() for CLOCK_REALTIME
    Date
    [ Upstream commit 81fb8736dd81da3fe94f28968dac60f392ec6746 ]

    clock_getres() in the vDSO library has to preserve the same behaviour
    of posix_get_hrtimer_res().

    In particular, posix_get_hrtimer_res() does:

    sec = 0;
    ns = hrtimer_resolution;

    where 'hrtimer_resolution' depends on whether or not high resolution
    timers are enabled, which is a runtime decision.

    The vDSO incorrectly returns the constant CLOCK_REALTIME_RES. Fix this
    by exposing 'hrtimer_resolution' in the vDSO datapage and returning that
    instead.

    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    [will: Use WRITE_ONCE(), move adr off COARSE path, renumber labels, use 'w' reg]
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/arm64/include/asm/vdso_datapage.h | 1 +
    arch/arm64/kernel/asm-offsets.c | 2 +-
    arch/arm64/kernel/vdso.c | 3 +++
    arch/arm64/kernel/vdso/gettimeofday.S | 7 +++----
    4 files changed, 8 insertions(+), 5 deletions(-)

    diff --git a/arch/arm64/include/asm/vdso_datapage.h b/arch/arm64/include/asm/vdso_datapage.h
    index 2b9a63771eda8..f89263c8e11af 100644
    --- a/arch/arm64/include/asm/vdso_datapage.h
    +++ b/arch/arm64/include/asm/vdso_datapage.h
    @@ -38,6 +38,7 @@ struct vdso_data {
    __u32 tz_minuteswest; /* Whacky timezone stuff */
    __u32 tz_dsttime;
    __u32 use_syscall;
    + __u32 hrtimer_res;
    };

    #endif /* !__ASSEMBLY__ */
    diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
    index 7f40dcbdd51d0..e10e2a5d9ddcf 100644
    --- a/arch/arm64/kernel/asm-offsets.c
    +++ b/arch/arm64/kernel/asm-offsets.c
    @@ -94,7 +94,7 @@ int main(void)
    DEFINE(CLOCK_REALTIME, CLOCK_REALTIME);
    DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);
    DEFINE(CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_RAW);
    - DEFINE(CLOCK_REALTIME_RES, MONOTONIC_RES_NSEC);
    + DEFINE(CLOCK_REALTIME_RES, offsetof(struct vdso_data, hrtimer_res));
    DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);
    DEFINE(CLOCK_MONOTONIC_COARSE,CLOCK_MONOTONIC_COARSE);
    DEFINE(CLOCK_COARSE_RES, LOW_RES_NSEC);
    diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
    index 2d419006ad433..ec0bb588d7553 100644
    --- a/arch/arm64/kernel/vdso.c
    +++ b/arch/arm64/kernel/vdso.c
    @@ -232,6 +232,9 @@ void update_vsyscall(struct timekeeper *tk)
    vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec;
    vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec;

    + /* Read without the seqlock held by clock_getres() */
    + WRITE_ONCE(vdso_data->hrtimer_res, hrtimer_resolution);
    +
    if (!use_syscall) {
    /* tkr_mono.cycle_last == tkr_raw.cycle_last */
    vdso_data->cs_cycle_last = tk->tkr_mono.cycle_last;
    diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
    index e8f60112818fc..856fee6d35129 100644
    --- a/arch/arm64/kernel/vdso/gettimeofday.S
    +++ b/arch/arm64/kernel/vdso/gettimeofday.S
    @@ -308,13 +308,14 @@ ENTRY(__kernel_clock_getres)
    ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne
    b.ne 1f

    - ldr x2, 5f
    + adr vdso_data, _vdso_data
    + ldr w2, [vdso_data, #CLOCK_REALTIME_RES]
    b 2f
    1:
    cmp w0, #CLOCK_REALTIME_COARSE
    ccmp w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
    b.ne 4f
    - ldr x2, 6f
    + ldr x2, 5f
    2:
    cbz x1, 3f
    stp xzr, x2, [x1]
    @@ -328,8 +329,6 @@ ENTRY(__kernel_clock_getres)
    svc #0
    ret
    5:
    - .quad CLOCK_REALTIME_RES
    -6:
    .quad CLOCK_COARSE_RES
    .cfi_endproc
    ENDPROC(__kernel_clock_getres)
    --
    2.20.1


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