On 2024-10-14 1:49 p.m., Peter Zijlstra wrote:
> On Mon, Oct 14, 2024 at 11:51:06AM -0400, Liang, Kan wrote:
>> On 2024-10-14 8:03 a.m., Peter Zijlstra wrote:
>>> On Thu, Aug 01, 2024 at 04:58:23AM +0000, Mingwei Zhang wrote:
>>>> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>>>>
>>>> There will be a dedicated interrupt vector for guests on some platforms,
>>>> e.g., Intel. Add an interface to switch the interrupt vector while
>>>> entering/exiting a guest.
>>>>
>>>> When PMI switch into a new guest vector, guest_lvtpc value need to be
>>>> reflected onto HW, e,g., guest clear PMI mask bit, the HW PMI mask
>>>> bit should be cleared also, then PMI can be generated continuously
>>>> for guest. So guest_lvtpc parameter is added into perf_guest_enter()
>>>> and switch_interrupt().
>>>>
>>>> At switch_interrupt(), the target pmu with PASSTHROUGH cap should
>>>> be found. Since only one passthrough pmu is supported, we keep the
>>>> implementation simply by tracking the pmu as a global variable.
>>>>
>>>> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>>>>
>>>> [Simplify the commit with removal of srcu lock/unlock since only one pmu is
>>>> supported.]
>>>>
>>>> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>>>> ---
>>>> include/linux/perf_event.h | 9 +++++++--
>>>> kernel/events/core.c | 36 ++++++++++++++++++++++++++++++++++--
>>>> 2 files changed, 41 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>>>> index 75773f9890cc..aeb08f78f539 100644
>>>> --- a/include/linux/perf_event.h
>>>> +++ b/include/linux/perf_event.h
>>>> @@ -541,6 +541,11 @@ struct pmu {
>>>> * Check period value for PERF_EVENT_IOC_PERIOD ioctl.
>>>> */
>>>> int (*check_period) (struct perf_event *event, u64 value); /* optional */
>>>> +
>>>> + /*
>>>> + * Switch the interrupt vectors, e.g., guest enter/exit.
>>>> + */
>>>> + void (*switch_interrupt) (bool enter, u32 guest_lvtpc); /* optional */
>>>> };
>>>
>>> I'm thinking the guets_lvtpc argument shouldn't be part of the
>>> interface. That should be PMU implementation data and accessed by the
>>> method implementation.
>>
>> I think the name of the perf_switch_interrupt() is too specific.
>> Here should be to switch the guest context. The interrupt should be just
>> part of the context. Maybe a interface as below
>>
>> void (*switch_guest_ctx) (bool enter, void *data); /* optional */
>
> I don't think you even need the data thing. For example, the x86/intel
> implementation can just look at a x86_pmu data field to find the magic
> value.
The new vector is created by KVM, not perf. So it cannot be found in the
x86_pmu data field. Perf needs it to update the interrupt vector so the
guest PMI can be handled by KVM directly.
Thanks,
Kan
