Re: [RESEND PATCH v5 2/6] perf/core: Use ioctl to communicate driver configuration to kernel

Greg KH
2018-12-19T08:31:43Z

On Mon, Dec 17, 2018 at 10:21:42AM -0700, Mathieu Poirier wrote:
> This patch adds the mechanic needed for user space to send PMU specific
> configuration to the kernel driver using an ioctl() command. That way
> events can keep track of options that don't fit in the perf_event_attr
> structure like the selection of a CoreSight sink to use for the session.
>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
> include/linux/perf_event.h | 38 ++++++++++++++++++++++++++
> kernel/events/core.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 105 insertions(+)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 53c500f0ca79..8e69b7e309e7 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -114,6 +114,14 @@ struct hw_perf_event_extra {
> int idx; /* index in shared_regs->regs[] */
> };
>
> +/*
> + * PMU driver configuration
> + */
> +struct pmu_drv_config {
> + void *config;
> + raw_spinlock_t lock;
> +};
> +
> /**
> * struct hw_perf_event - performance event hardware details:
> */
> @@ -178,6 +186,9 @@ struct hw_perf_event {
> /* Last sync'ed generation of filters */
> unsigned long addr_filters_gen;
>
> + /* PMU driver configuration */
> + struct pmu_drv_config drv_config;
> +
> /*
> * hw_perf_event::state flags; used to track the PERF_EF_* state.
> */
> @@ -447,6 +458,17 @@ struct pmu {
> * Filter events for PMU-specific reasons.
> */
> int (*filter_match) (struct perf_event *event); /* optional */
> +
> + /*
> + * Validate complex PMU configuration that don't fit in the
> + * perf_event_attr struct. Returns a PMU specific pointer or an error
> + * value < 0.
> + *
> + * As with addr_filters_validate(), runs in the context of the ioctl()
> + * process and is not serialized with the rest of the PMU callbacks.
> + */
> + void *(*drv_config_validate) (struct perf_event *event,
> + u64 value);
> };
>
> enum perf_addr_filter_action_t {
> @@ -1235,6 +1257,11 @@ static inline bool has_addr_filter(struct perf_event *event)
> return event->pmu->nr_addr_filters;
> }
>
> +static inline bool has_drv_config(struct perf_event *event)
> +{
> + return event->pmu->drv_config_validate;
> +}
> +
> /*
> * An inherited event uses parent's filters
> */
> @@ -1249,6 +1276,17 @@ perf_event_addr_filters(struct perf_event *event)
> return ifh;
> }
>
> +static inline struct pmu_drv_config *
> +perf_event_get_drv_config(struct perf_event *event)
> +{
> + struct pmu_drv_config *cfg = &event->hw.drv_config;
> +
> + if (event->parent)
> + cfg = &event->parent->hw.drv_config;
> +
> + return cfg;
> +}
> +
> extern void perf_event_addr_filters_sync(struct perf_event *event);
>
> extern int perf_output_begin(struct perf_output_handle *handle,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 84530ab358c3..af7a53c97744 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5003,6 +5003,8 @@ static inline int perf_fget_light(int fd, struct fd *p)
> static int perf_event_set_output(struct perf_event *event,
> struct perf_event *output_event);
> static int perf_event_set_filter(struct perf_event *event, void __user *arg);
> +static int perf_event_set_drv_config(struct perf_event *event,
> + void __user *arg);
> static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);
> static int perf_copy_attr(struct perf_event_attr __user *uattr,
> struct perf_event_attr *attr);
> @@ -5089,6 +5091,10 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
>
> return perf_event_modify_attr(event, &new_attr);
> }
> +
> + case PERF_EVENT_IOC_SET_DRV_CONFIG:
> + return perf_event_set_drv_config(event, (void __user *)arg);
> +
> default:
> return -ENOTTY;
> }
> @@ -9128,6 +9134,66 @@ static int perf_event_set_filter(struct perf_event *event, void __user *arg)
> return ret;
> }
>
> +static void perf_drv_config_replace(struct perf_event *event, void *drv_data)
> +{
> + unsigned long flags;
> + struct pmu_drv_config *drv_config = &event->hw.drv_config;
> +
> + if (!has_drv_config(event))
> + return;
> +
> + /* Children take their configuration from their parent */
> + if (event->parent)
> + return;
> +
> + /* Make sure the PMU doesn't get a handle on the data */
> + raw_spin_lock_irqsave(&drv_config->lock, flags);
> + drv_config->config = drv_data;
> + raw_spin_unlock_irqrestore(&drv_config->lock, flags);
> +}
> +
> +static int
> +perf_event_process_drv_config(struct perf_event *event, u64 value)
> +{
> + int ret = -EINVAL;
> + void *drv_data;
> +
> + /* Make sure ctx.mutex is held */
> + lockdep_assert_held(&event->ctx->mutex);
> +
> + /* Children take their configuration from their parent */
> + if (WARN_ON_ONCE(event->parent))
> + goto out;
> +
> + drv_data = event->pmu->drv_config_validate(event, value);
> + if (IS_ERR(drv_data)) {
> + ret = PTR_ERR(drv_data);
> + goto out;
> + }
> +
> + perf_drv_config_replace(event, drv_data);
> +
> + ret = 0;
> +out:
> + return ret;
> +}
> +
> +static int perf_event_set_drv_config(struct perf_event *event, void __user *arg)
> +{
> + int ret;
> + u64 value;
> +
> + if (!has_drv_config(event))
> + return -EINVAL;
> +
> + if (copy_from_user(&value, arg, sizeof(value)))
> + return -EFAULT;

You are just sending in a pointer to a u64? Why not just pass a u64
directly instead? Why is a pointer needed here?

thanks,

greg k-h