From: Jinrong Liang <cloudliang@xxxxxxxxxxx> From: Jinrong Liang <cloudliang@xxxxxxxxxxx> Update the documentation for the KVM_SET_PMU_EVENT_FILTER ioctl to include a detailed description of how fixed performance events are handled in the pmu filter. The action and fixed_counter_bitmap members of the pmu filter to determine whether fixed performance events can be programmed by the guest. This information is helpful for correctly configuring the fixed_counter_bitmap and action fields to filter fixed performance events. Suggested-by: Like Xu <likexu@xxxxxxxxxxx> Reported-by: kernel test robot <lkp@xxxxxxxxx> Link: https://lore.kernel.org/oe-kbuild-all/202304150850.rx4UDDsB-lkp@xxxxxxxxx Signed-off-by: Jinrong Liang <cloudliang@xxxxxxxxxxx> --- Documentation/virt/kvm/api.rst | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index a69e91088d76..b5836767e0e7 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5122,6 +5122,27 @@ Valid values for 'action':: #define KVM_PMU_EVENT_ALLOW 0 #define KVM_PMU_EVENT_DENY 1 +Via this API, KVM userspace can also control the behavior of the VM's fixed +counters (if any) by configuring the "action" and "fixed_counter_bitmap" fields. + +Specifically, KVM follows the following pseudo-code when determining whether to +allow the guest FixCtr[i] to count its pre-defined fixed event:: + + FixCtr[i]_is_allowed = (action == ALLOW) && (bitmap & BIT(i)) || + (action == DENY) && !(bitmap & BIT(i)); + FixCtr[i]_is_denied = !FixCtr[i]_is_allowed; + +Note once this API interface is called, the default zero value of the field +"fixed_counter_bitmap" will implicitly affect all fixed counters, even if it's +expected to be used only to control the events on generic counters. + +In addition, pre-defined performance events on the fixed counters already have +event_select and unit_mask values defined, which means userspace can also +control fixed counters by configuring "action"+ "events" fields. + +When there is a contradiction between these two polices, the fixed performance +counter will only follow the rule of the pseudo-code above. + 4.121 KVM_PPC_SVM_OFF --------------------- -- 2.31.1
