From b35babd3abea081de0611ce0d5b85281c18c52c7 Mon Sep 17 00:00:00 2001 From: Jinrong Liang Date: Wed, 31 May 2023 15:50:52 +0800 Subject: [PATCH] KVM: x86/pmu: Add documentation for fixed ctr on PMU filter 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 Reported-by: kernel test robot Link: https://lore.kernel.org/oe-kbuild-all/202304150850.rx4UDDsB-lkp@intel.com Signed-off-by: Jinrong Liang Link: https://lore.kernel.org/r/20230531075052.43239-1-cloudliang@tencent.com Signed-off-by: Sean Christopherson --- Documentation/virt/kvm/api.rst | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index fda7f7b0115e..67347d827242 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5124,6 +5124,24 @@ 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; + +KVM always consumes fixed_counter_bitmap, it's userspace's responsibility to +ensure fixed_counter_bitmap is set correctly, e.g. if userspace wants to define +a filter that only affects general purpose counters. + +Note, the "events" field also applies to fixed counters' hardcoded event_select +and unit_mask values. "fixed_counter_bitmap" has higher priority than "events" +if there is a contradiction between the two. + 4.121 KVM_PPC_SVM_OFF ---------------------