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KVM: x86/pmu: Add documentation for fixed ctr on PMU filter

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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@tencent.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304150850.rx4UDDsB-lkp@intel.com
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
Link: https://lore.kernel.org/r/20230531075052.43239-1-cloudliang@tencent.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Jinrong Liang 2023-05-31 15:50:52 +08:00 committed by Sean Christopherson
parent 78b5605d44
commit b35babd3ab
1 changed files with 18 additions and 0 deletions
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18
Documentation/virt/kvm/api.rst
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@ -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
---------------------