Re: [PATCH v3 5/5] KVM: arm64: Document PMU filtering API

[Auger Eric <eric.auger@redhat.com>]

Hi Marc,

On 9/8/20 9:58 AM, Marc Zyngier wrote:
> Add a small blurb describing how the event filtering API gets used.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  Documentation/virt/kvm/devices/vcpu.rst | 46 +++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
> index ca374d3fe085..203b91e93151 100644
> --- a/Documentation/virt/kvm/devices/vcpu.rst
> +++ b/Documentation/virt/kvm/devices/vcpu.rst
> @@ -55,6 +55,52 @@ Request the initialization of the PMUv3.  If using the PMUv3 with an in-kernel
>  virtual GIC implementation, this must be done after initializing the in-kernel
>  irqchip.
>  
> +1.3 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_FILTER
> +---------------------------------------
> +
> +:Parameters: in kvm_device_attr.addr the address for a PMU event filter is a
> +             pointer to a struct kvm_pmu_event_filter
> +
> +:Returns:
> +
> +	 =======  ======================================================
> +	 -ENODEV: PMUv3 not supported or GIC not initialized
> +	 -ENXIO:  PMUv3 not properly configured or in-kernel irqchip not
> +	 	  configured as required prior to calling this attribute
> +	 -EBUSY:  PMUv3 already initialized
> +	 -EINVAL: Invalid filter range
> +	 =======  ======================================================
> +
> +Request the installation of a PMU event filter describe as follows:
> +
> +struct kvm_pmu_event_filter {
> +	__u16	base_event;
> +	__u16	nevents;
> +
> +#define KVM_PMU_EVENT_ALLOW	0
> +#define KVM_PMU_EVENT_DENY	1
> +
> +	__u8	action;
> +	__u8	pad[3];
> +};
> +
> +A filter range is defined as the range [@base_event, @base_event + @nevents[,
> +together with an @action (KVM_PMU_EVENT_ALLOW or KVM_PMU_EVENT_DENY). The
> +first registered range defines the global policy (global ALLOW if the first
> +@action is DENY, global DENY if the first @action is ALLOW). Multiple ranges
> +can be programmed, and must fit within the event space defined by the PMU
> +architecture (10 bits on ARMv8.0, 16 bits from ARMv8.1 onwards).
> +
> +Note: "Cancelling" a filter by registering the opposite action for the same
> +range doesn't change the default action. For example, installing an ALLOW
> +filter for event range [0:10] as the first filter and then applying a DENY
> +action for the same range will leave the whole range as disabled.
> +
> +Restrictions: Event 0 (SW_INCR) is never filtered, as it doesn't count a
> +hardware event. Filtering event 0x1E (CHAIN) has no effect either, as it
> +isn't strictly speaking an event. Filtering the cycle counter is possible
> +using event 0x11 (CPU_CYCLES).
Oh I see here you did comment it in the uapi.

Thanks

Eric
> +
>  
>  2. GROUP: KVM_ARM_VCPU_TIMER_CTRL
>  =================================
>