Re: [PATCH v7] arm/kvm: Enable support for KVM_ARM_VCPU_PMU_V3_FILTER

[Daniel P . Berrangé]

On Wed, Feb 21, 2024 at 01:34:31AM -0500, Shaoqin Huang wrote:

> diff --git a/docs/system/arm/cpu-features.rst 
> b/docs/system/arm/cpu-features.rst
> index a5fb929243..7c8f6a60ef 100644
> --- a/docs/system/arm/cpu-features.rst
> +++ b/docs/system/arm/cpu-features.rst
> @@ -204,6 +204,29 @@ the list of KVM VCPU features and their descriptions.
>    the guest scheduler behavior and/or be exposed to the guest
>    userspace.
>  
> +``kvm-pmu-filter``
> +  By default kvm-pmu-filter is disabled. This means that by default all pmu
> +  events will be exposed to guest.
> +
> +  KVM implements PMU Event Filtering to prevent a guest from being able to
> +  sample certain events. It depends on the KVM_ARM_VCPU_PMU_V3_FILTER
> +  attribute supported in KVM. It has the following format:
> +
> +  kvm-pmu-filter="{A,D}:start-end[;{A,D}:start-end...]"
> +
> +  The A means "allow" and D means "deny", start is the first event of the
> +  range and the end is the last one. The first registered range defines
> +  the global policy(global ALLOW if the first @action is DENY, global DENY
> +  if the first @action is ALLOW). The start and end only support hexadecimal
> +  format. For example:
> +
> +  kvm-pmu-filter="A:0x11-0x11;A:0x23-0x3a;D:0x30-0x30"
> +
> +  Since the first action is allow, we have a global deny policy. It
> +  will allow event 0x11 (The cycle counter), events 0x23 to 0x3a are
> +  also allowed except the event 0x30 which is denied, and all the other
> +  events are denied.


Can you document whether the policy evaluation stops at the first
matching range, or checks all ranges

ie, if you have

  kvm-pmu-filter="A:0x1-0x9;D=0x7-0x7"

will an input of '0x7' be allowed (because it matches the
first range and stops), or denied (because the second range
overrides the result of the first)



With regards,
Daniel
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