On 5/15/2025 7:30 AM, Sean Christopherson wrote:
> On Mon, Mar 24, 2025, Mingwei Zhang wrote:
>> From: Kan Liang <kan.li...@linux.intel.com>
>>
>> When entering/exiting a guest, some contexts for a guest have to be
>> switched. For examples, there is a dedicated interrupt vector for
>> guests on Intel platforms.
>>
>> 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_guest_ctx().
>>
>> Add a dedicated list to track all the pmus with the PASSTHROUGH cap, which
>> may require switching the guest context. It can avoid going through the
>> huge pmus list.
>>
>> Suggested-by: Peter Zijlstra (Intel) <pet...@infradead.org>
>> Signed-off-by: Kan Liang <kan.li...@linux.intel.com>
>> Signed-off-by: Mingwei Zhang <mizh...@google.com>
>> ---
>> include/linux/perf_event.h | 17 +++++++++++--
>> kernel/events/core.c | 51 +++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 65 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 37187ee8e226..58c1cf6939bf 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -584,6 +584,11 @@ struct pmu {
>> * Check period value for PERF_EVENT_IOC_PERIOD ioctl.
>> */
>> int (*check_period) (struct perf_event *event, u64 value);
>> /* optional */
>> +
>> + /*
>> + * Switch guest context when a guest enter/exit, e.g., interrupt
>> vectors.
>> + */
>> + void (*switch_guest_ctx) (bool enter, void *data); /* optional */
> IMO, putting this in "struct pmu" is unnecessarily convoluted and complex,
> and a
> poor fit for what needs to be done. The only usage of the hook is for the
> CPU to
> swap the LVTPC, and the @data payload communicates exactly that. I.e. this
> has
> one user, and can't reasonably be extended to other users without some
> ugliness.
>
> And if by some miracle there's no CPU pmu in perf, KVM's mediated PMU still
> needs
> to swap to its PMI IRQ. So rather than per-PMU hook along with a list and a
> spinlock, just make this an arch hook. And if all of the mediated PMU code is
> guarded by a Kconfig, then perf doesn't even needs __weak stubs.
Sounds good for me.
>
