[PATCH v2] KVM: arm64: Fix hyp_trace clock disabling

[Fuad Tabba]

Hi Vincent,

On Wed, 15 Jul 2026 at 11:51, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> Fix the disable path in hyp_trace_clock_enable(), which fell through to
> re-initialize and reschedule the clock after cancelling the work. Return
> early instead.
>
> While at it, cleanup hyp_trace_clock::lock which is unused and
> hyp_trace_clock::running which is redundant: the trace_remote framework
> already serializes calls to the callback enable_tracing.

Although the cleanup and the fix are to the same commit, could this be
split into the fix and the lock/running cleanup as a separate patch?
Since b22888917fa41 is already in a released kernel, the fix will
likely go to stable, and it'd be nice to keep that backport to just
the behavioural change.

Cheers,
/fuad

>
> Fixes: b22888917fa4 ("KVM: arm64: Sync boot clock with the nVHE/pKVM hyp")
> Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
>
> ---
>
> v1 -> v2:
>   * Rollback hyp_trace_clock_enable() on __tracing_enable error (Sashiko)
>
> v1: https://lore.kernel.org/all/alczBmnItMwq8xj4@google.com/
>
> diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
> index 2411b4c32932..9bfa368dd841 100644
> --- a/arch/arm64/kvm/hyp_trace.c
> +++ b/arch/arm64/kvm/hyp_trace.c
> @@ -37,8 +37,6 @@ static struct hyp_trace_clock {
>         u32                     shift;
>         struct delayed_work     work;
>         struct completion       ready;
> -       struct mutex            lock;
> -       bool                    running;
>  } hyp_clock;
>
>  static void __hyp_clock_work(struct work_struct *work)
> @@ -110,12 +108,9 @@ static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool enabl
>  {
>         struct system_time_snapshot snap;
>
> -       if (hyp_clock->running == enable)
> -               return;
> -
>         if (!enable) {
>                 cancel_delayed_work_sync(&hyp_clock->work);
> -               hyp_clock->running = false;
> +               return;
>         }
>
>         ktime_get_snapshot_id(CLOCK_BOOTTIME, &snap);
> @@ -128,7 +123,6 @@ static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool enabl
>         INIT_DELAYED_WORK(&hyp_clock->work, __hyp_clock_work);
>         schedule_delayed_work(&hyp_clock->work, msecs_to_jiffies(CLOCK_INIT_MS));
>         wait_for_completion(&hyp_clock->ready);
> -       hyp_clock->running = true;
>  }
>
>  /* Access to this struct within the trace_remote_callbacks are protected by the trace_remote lock */
> @@ -304,9 +298,15 @@ static void hyp_trace_unload(struct trace_buffer_desc *desc, void *priv)
>
>  static int hyp_trace_enable_tracing(bool enable, void *priv)
>  {
> +       int ret;
> +
>         hyp_trace_clock_enable(&hyp_clock, enable);
>
> -       return kvm_call_hyp_nvhe(__tracing_enable, enable);
> +       ret = kvm_call_hyp_nvhe(__tracing_enable, enable);
> +       if (ret)
> +               hyp_trace_clock_enable(&hyp_clock, !enable);
> +
> +       return ret;
>  }
>
>  static int hyp_trace_swap_reader_page(unsigned int cpu, void *priv)
>
> base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
> --
> 2.55.0.141.g00534a21ce-goog
>