Re: [PATCH v4] arm/kvm: Enable support for KVM_ARM_VCPU_PMU_V3_FILTER

[Sebastian Ott]

On Thu, 14 Dec 2023, Eric Auger wrote:
> On 12/7/23 11:36, Shaoqin Huang wrote:
> > +    if (kvm_vcpu_ioctl(cs, KVM_HAS_DEVICE_ATTR, &attr)) {
> > +        warn_report("The kernel doesn't support the PMU Event Filter!\n");
> > +        return;
> > +    }
> > +
> > +    /* The filter only needs to be initialized for 1 vcpu. */
> Are you sure? This is a per vcpu device ctrl. Where is it written in the
> doc that this shall not be called for each vcpu

The interface is per vcpu but the filters are actually managed per vm
(kvm->arch.pmu_filter). From (kernel) commit 6ee7fca2a ("KVM: arm64: Add 
KVM_ARM_VCPU_PMU_V3_SET_PMU attribute"):
 To ensure that KVM doesn't expose an asymmetric system to the guest, the
 PMU set for one VCPU will be used by all other VCPUs. Once a VCPU has run,
 the PMU cannot be changed in order to avoid changing the list of available
 events for a VCPU, or to change the semantics of existing events.

Sebastian