Commit b35babd3 authored by Jinrong Liang's avatar Jinrong Liang Committed by Sean Christopherson
Browse files

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: default avatarLike Xu <likexu@tencent.com>
Reported-by: default avatarkernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304150850.rx4UDDsB-lkp@intel.com


Signed-off-by: default avatarJinrong Liang <cloudliang@tencent.com>
Link: https://lore.kernel.org/r/20230531075052.43239-1-cloudliang@tencent.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 78b5605d

Documentation/virt/kvm/api.rst

+18 −0
Original line number Diff line number Diff line
@@ -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

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