2023-05-31 07:56:08

by Jinrong Liang

Subject: [PATCH v3] KVM: x86/pmu: Add documentation for fixed ctr on PMU filter

From: Jinrong Liang <[email protected]>

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 <[email protected]>
Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/oe-kbuild-all/[email protected]
Signed-off-by: Jinrong Liang <[email protected]>
---

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/[email protected]

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

2023-09-29 00:23:19

by Sean Christopherson

Subject: Re: [PATCH v3] KVM: x86/pmu: Add documentation for fixed ctr on PMU filter

On Wed, 31 May 2023 15:50:52 +0800, Jinrong Liang wrote:
> 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.
>
> [...]

Applied to kvm-x86 docs, thanks!

[1/1] KVM: x86/pmu: Add documentation for fixed ctr on PMU filter
https://github.com/kvm-x86/linux/commit/b35babd3abea

--
https://github.com/kvm-x86/linux/tree/next