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> --- v3: - Rebased to 5c291b93e5d6(tag: kvm-x86-next-2023.04.26) - Revise documentation to enhance user understanding. (Sean) - Post this patch separately from the selftests changes. (Sean) v2: - Wrap the code from the documentation in a block of code; (Bagas Sanjaya) v1: https://lore.kernel.org/kvm/20230414110056.19665-5-cloudliang@xxxxxxxxxxx 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 a69e91088d76..9f680eb89b2b 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5122,6 +5122,24 @@ 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 --------------------- base-commit: 5c291b93e5d665380dbecc6944973583f9565ee5 -- 2.31.1
