Re: [PATCH] perf/arm_smmuv3: Omit the two judgements which done in framework

[Yang Jialong 杨佳龙]

在 2024/2/10 0:32, Robin Murphy 写道:
> On 2024-02-09 4:09 pm, Will Deacon wrote:
> > On Thu, Dec 21, 2023 at 05:38:01PM +0800, JiaLong.Yang wrote:
> > > 'event->attr.type != event->pmu->type' has been done in
> > > core.c::perf_init_event() ,core.c::perf_event_modify_attr(), etc.
> > >
> > > This PMU is an uncore one. The core framework has disallowed
> > > uncore-task events. So the judgement to event->cpu < 0 is no mean.
> >
> > It would be great to refer to the changes which added those checks to
> > the perf core code. From reading the code myself, I can't convince myself
> > that perf_try_init_event() won't call into the driver.
> >
> > > The two judgements have been done in kernel/events/core.c
> > >
> > > Signed-off-by: JiaLong.Yang <jialong.yang@xxxxxxxxxxxx>
> > > ---
> > >   drivers/perf/arm_smmuv3_pmu.c | 8 --------
> > >   1 file changed, 8 deletions(-)
> >
> > It looks like _many_ perf drivers have these checks, so if they really
> > aren't needed, we can clean this up bveyond SMMU. However, as I said
> > above, I'm not quite convinced we can drop them.
>
> Right, I think the logic prevents events with a specific PMU type being 
> offered to other PMUs, but as far as I'm aware doesn't apply the other 
> way round to stop generic events (PERF_TYPE_HARDWARE etc.) being offered 
> to all PMUs, so it's those that system PMUs need to reject. >
> It's been on my wishlist for a long time to have a capability flag to 
> say "I don't handle generic events, please only ever give me events of 
> my exact type" so we *can* truly factor this into the core.


It's core framework's responsible to differ generic events and others, 
or uncore pmu and core pmu.
Here we have flag PERF_TYPE_HARDWARE, PERF_TYPE_HW_CACHE, 
PERF_PMU_CAP_EXTENDED_HW_TYPE doing this.

again:
        rcu_read_lock();
        pmu = idr_find(&pmu_idr, type);
        rcu_read_unlock();
        if (pmu) {
                if (event->attr.type != type && type != PERF_TYPE_RAW &&
                    !(pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE))
                        goto fail; /* generic event with no ability pmu */
This can avoid driver code (event->attr.type != event->pmu->type).

And, code:
if (pmu->task_ctx_nr == perf_invalid_context && (task || cgroup_fd != -1)) {
	err = -EINVAL;
	goto err_pmu;
}
can promise not uncore-task event.

We should confirm that uncore event should be cpu >= 0.

> Thanks,
> Robin.