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    Subject[PATCH 4.20 040/111] xen: Fix x86 sched_clock() interface for xen
    Date
    4.20-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Juergen Gross <jgross@suse.com>

    commit 867cefb4cb1012f42cada1c7d1f35ac8dd276071 upstream.

    Commit f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable'
    sched_clock() interface") broke Xen guest time handling across
    migration:

    [ 187.249951] Freezing user space processes ... (elapsed 0.001 seconds) done.
    [ 187.251137] OOM killer disabled.
    [ 187.251137] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
    [ 187.252299] suspending xenstore...
    [ 187.266987] xen:grant_table: Grant tables using version 1 layout
    [18446743811.706476] OOM killer enabled.
    [18446743811.706478] Restarting tasks ... done.
    [18446743811.720505] Setting capacity to 16777216

    Fix that by setting xen_sched_clock_offset at resume time to ensure a
    monotonic clock value.

    [boris: replaced pr_info() with pr_info_once() in xen_callback_vector()
    to avoid printing with incorrect timestamp during resume (as we
    haven't re-adjusted the clock yet)]

    Fixes: f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface")
    Cc: <stable@vger.kernel.org> # 4.11
    Reported-by: Hans van Kranenburg <hans.van.kranenburg@mendix.com>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Tested-by: Hans van Kranenburg <hans.van.kranenburg@mendix.com>
    Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/xen/time.c | 12 +++++++++---
    drivers/xen/events/events_base.c | 2 +-
    2 files changed, 10 insertions(+), 4 deletions(-)

    --- a/arch/x86/xen/time.c
    +++ b/arch/x86/xen/time.c
    @@ -361,8 +361,6 @@ void xen_timer_resume(void)
    {
    int cpu;

    - pvclock_resume();
    -
    if (xen_clockevent != &xen_vcpuop_clockevent)
    return;

    @@ -379,12 +377,15 @@ static const struct pv_time_ops xen_time
    };

    static struct pvclock_vsyscall_time_info *xen_clock __read_mostly;
    +static u64 xen_clock_value_saved;

    void xen_save_time_memory_area(void)
    {
    struct vcpu_register_time_memory_area t;
    int ret;

    + xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
    +
    if (!xen_clock)
    return;

    @@ -404,7 +405,7 @@ void xen_restore_time_memory_area(void)
    int ret;

    if (!xen_clock)
    - return;
    + goto out;

    t.addr.v = &xen_clock->pvti;

    @@ -421,6 +422,11 @@ void xen_restore_time_memory_area(void)
    if (ret != 0)
    pr_notice("Cannot restore secondary vcpu_time_info (err %d)",
    ret);
    +
    +out:
    + /* Need pvclock_resume() before using xen_clocksource_read(). */
    + pvclock_resume();
    + xen_sched_clock_offset = xen_clocksource_read() - xen_clock_value_saved;
    }

    static void xen_setup_vsyscall_time_info(void)
    --- a/drivers/xen/events/events_base.c
    +++ b/drivers/xen/events/events_base.c
    @@ -1650,7 +1650,7 @@ void xen_callback_vector(void)
    xen_have_vector_callback = 0;
    return;
    }
    - pr_info("Xen HVM callback vector for event delivery is enabled\n");
    + pr_info_once("Xen HVM callback vector for event delivery is enabled\n");
    alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
    xen_hvm_callback_vector);
    }

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