[PATCH 11/21] KVM: arm64: Context swap Partitioned PMU guest registers

[James Clark]

On 12/06/2026 20:28, Colton Lewis wrote:
> Save and restore newly untrapped registers that can be directly
> accessed by the guest when the PMU is partitioned.
> 
> * PMEVCNTRn_EL0
> * PMCCNTR_EL0
> * PMSELR_EL0
> * PMCR_EL0
> * PMCNTEN_EL0
> * PMINTEN_EL1
> 
> If we know we are not partitioned (that is, using the emulated vPMU),
> then return immediately. A later patch will make this lazy so the
> context swaps don't happen unless the guest has accessed the PMU.
> 
> PMEVTYPER is handled in a following patch since we must apply the KVM
> event filter before writing values to hardware.
> 
> PMOVS guest counters are cleared to avoid the possibility of
> generating spurious interrupts when PMINTEN is written. This is fine
> because the virtual register for PMOVS is always the canonical value.
> 
> Signed-off-by: Colton Lewis <coltonlewis at google.com>
> ---
>   arch/arm/include/asm/arm_pmuv3.h |   4 +
>   arch/arm64/kvm/arm.c             |   2 +
>   arch/arm64/kvm/pmu-direct.c      | 183 +++++++++++++++++++++++++++++++
>   include/kvm/arm_pmu.h            |  16 +++
>   4 files changed, 205 insertions(+)
> 

[...]

> +
> +/**
> + * kvm_pmu_put() - Put untrapped PMU registers
> + * @vcpu: Pointer to struct kvm_vcpu
> + *
> + * Put all untrapped PMU registers from the VCPU into the PCPU. Mask
> + * to only bits belonging to guest-reserved counters and leave
> + * host-reserved counters alone in bitmask registers.
> + */
> +void kvm_pmu_put(struct kvm_vcpu *vcpu)
> +{
> +	struct arm_pmu *pmu;
> +	unsigned long guest_counters;
> +	unsigned long flags;
> +	u64 mask;
> +	u8 i;
> +	u64 val;
> +
> +	/*
> +	 * If we aren't guest-owned then we know the guest is not
> +	 * accessing the PMU anyway, so no need to bother with the
> +	 * swap.
> +	 */
> +	if (!kvm_pmu_is_partitioned(vcpu->kvm))
> +		return;
> +
> +	preempt_disable();
> +
> +	pmu = vcpu->kvm->arch.arm_pmu;
> +	guest_counters = kvm_pmu_guest_counter_mask(pmu);
> +
> +	for_each_set_bit(i, &guest_counters, ARMPMU_MAX_HWEVENTS) {
> +		if (i == ARMV8_PMU_CYCLE_IDX)
> +			val = read_pmccntr();
> +		else
> +			val = read_pmevcntrn(i);
> +
> +		__vcpu_assign_sys_reg(vcpu, PMEVCNTR0_EL0 + i, val);
> +	}
> +
> +	val = read_sysreg(pmselr_el0);
> +	__vcpu_assign_sys_reg(vcpu, PMSELR_EL0, val);
> +
> +	val = read_sysreg(pmcr_el0);
> +	__vcpu_assign_sys_reg(vcpu, PMCR_EL0, val);
> +
> +	/* Mask these to only save the guest relevant bits. */
> +	mask = kvm_pmu_guest_counter_mask(pmu);
> +
> +	val = read_sysreg(pmcntenset_el0);
> +	__vcpu_assign_sys_reg(vcpu, PMCNTENSET_EL0, val & mask);
> +
> +	val = read_sysreg(pmintenset_el1);
> +	__vcpu_assign_sys_reg(vcpu, PMINTENSET_EL1, val & mask);
> +
> +	/* Save pending guest hardware overflows. */
> +	local_irq_save(flags);
> +	val = read_sysreg(pmovsset_el0);
> +	__vcpu_rmw_sys_reg(vcpu, PMOVSSET_EL0, |=, val & mask);
> +	write_sysreg(val & mask, pmovsclr_el0);
> +	local_irq_restore(flags);
> +
> +	/* Stop guest counters and disable interrupts in hardware. */
> +	write_sysreg(mask, pmcntenclr_el0);
> +	write_sysreg(mask, pmintenclr_el1);
> +
> +	kvm_pmu_set_guest_counters(pmu, 0);

Hi Colton,

This function doesn't get added until "KVM: arm64: Apply dynamic guest 
counter reservations" a few commits later.

kvm_pmu_guest_counter_mask() is also used in a commit before it's added.