On Thu, May 15, 2025, Kan Liang wrote:
> On 2025-05-14 7:19 p.m., Sean Christopherson wrote:
> >> This naming is confusing on purpose? Pick either guest/host and stick
> >> with it.
> >
> > +1. I also think the inner perf_host_{enter,exit}() helpers are superflous.
> > These flows
> >
> > After a bit of hacking, and with a few spoilers, this is what I ended up
> > with
> > (not anywhere near fully tested). I like following KVM's
> > kvm_xxx_{load,put}()
> > nomenclature to tie everything together, so I went with "guest" instead of
> > "host"
> > even though the majority of work being down is to shedule out/in host
> > context.
> >
> > /* When loading a guest's mediated PMU, schedule out all exclude_guest
> > events. */
> > void perf_load_guest_context(unsigned long data)
> > {
> > struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> >
> > lockdep_assert_irqs_disabled();
> >
> > perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> >
> > if (WARN_ON_ONCE(__this_cpu_read(guest_ctx_loaded)))
> > goto unlock;
> >
> > perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
> > ctx_sched_out(&cpuctx->ctx, NULL, EVENT_GUEST);
> > perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
> > if (cpuctx->task_ctx) {
> > perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
> > task_ctx_sched_out(cpuctx->task_ctx, NULL, EVENT_GUEST);
> > perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
> > }
> >
> > arch_perf_load_guest_context(data);
> >
> > __this_cpu_write(guest_ctx_loaded, true);
> >
> > unlock:
> > perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> > }
> > EXPORT_SYMBOL_GPL(perf_load_guest_context);
> >
> > void perf_put_guest_context(void)
> > {
> > struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> >
> > lockdep_assert_irqs_disabled();
> >
> > perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> >
> > if (WARN_ON_ONCE(!__this_cpu_read(guest_ctx_loaded)))
> > goto unlock;
> >
> > arch_perf_put_guest_context();
>
> It will set the guest_ctx_loaded to false.
> The update_context_time() invoked in the perf_event_sched_in() will not
> get a chance to update the guest time.
The guest_ctx_loaded in arch/x86/events/core.c is a different variable, it just
happens to have the same name.
It's completely gross, but exposing guest_ctx_loaded outside of
kernel/events/core.c
didn't seem like a great alternative. If we wanted to use a single variable,
then the writes in arch_perf_{load,put}_guest_context() can simply go away.
