Re: [PATCH v5 21/24] KVM: arm64: Inject recorded guest interrupts

Oliver Upton
2025-12-15T17:50:25Z

On Fri, Dec 12, 2025 at 10:55:06PM +0000, Colton Lewis wrote:
> Oliver Upton <oupton@kernel.org> writes:
>
> > In no situation should KVM be injecting a "recorded" IRQ. The overflow
> > condition of the PMU is well defined in the architecture and we should
> > implement *exactly* that.
>
> When I say "record" I just meant "updating the virtual overflow register
> to reflect an overflow".

Right, consider changing the shortlog to read more along the lines of
"detect overflows for partitioned PMU" or similar.

> > On Tue, Dec 09, 2025 at 08:51:18PM +0000, Colton Lewis wrote:
> > > +/**
> > > + * kvm_pmu_part_overflow_status() - Determine if any guest counters
> > > have overflowed
> > > + * @vcpu: Ponter to struct kvm_vcpu
> > > + *
> > > + * Determine if any guest counters have overflowed and therefore an
> > > + * IRQ needs to be injected into the guest.
> > > + *
> > > + * Return: True if there was an overflow, false otherwise
> > > + */
> > > +bool kvm_pmu_part_overflow_status(struct kvm_vcpu *vcpu)
> > > +{
> > > + struct arm_pmu *pmu = vcpu->kvm->arch.arm_pmu;
> > > + u64 mask = kvm_pmu_guest_counter_mask(pmu);
> > > + u64 pmovs = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
> > > + u64 pmint = read_pmintenset();
> > > + u64 pmcr = read_pmcr();
>
> > How do we know that the vPMU has been loaded on the CPU at this point?
>
> Because this is only called by kvm_pmu_update_state which is only called
> by kvm_pmu_update_state <- kvm_pmu_{flush,sync}_hwstate <-
> kvm_arch_vcpu_ioctl_run after a vcpu_load.

That's assuming the PMU is loaded eagerly which I thought we agreed it
would not be.

Thanks,
Oliver