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

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Message-ID: <aTioEWHu0ZbFCjR6@kernel.org>
Date: Tue, 9 Dec 2025 14:52:01 -0800
From: Oliver Upton <oupton@...nel.org>
To: Colton Lewis <coltonlewis@...gle.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Mingwei Zhang <mizhang@...gle.com>, Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Mark Rutland <mark.rutland@....com>, Shuah Khan <shuah@...nel.org>,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 21/24] KVM: arm64: Inject recorded guest interrupts

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.

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?

> +
> +	return (pmcr & ARMV8_PMU_PMCR_E) && (mask & pmovs & pmint);
> +}

I'd rather reuse kvm_pmu_overflow_status(), relying on the accessors to
abstract away the implementation / location of the guest PMU context.

Thanks,
Oliver