Re: [PATCH v11 08/21] Revert "KVM: arm64: PMU: Reload when resetting"

[Oliver Upton <oupton@kernel.org>]

Hi Akihiko,

On Sun, Sep 20, 2026 at 08:15:49PM +0900, Akihiko Odaki wrote:
> This reverts commit fe53538069bb4f625bc8734103ba044a83138fea.
> 
> Restore PMU event teardown before system-register reset so existing
> perf events cannot retain configuration from the previous run. All
> counters are disabled by the reset PMCR_EL0 and MDCR_EL2 values, so
> reset does not need to request a PMU reload.

Sorry, I'm not following the intent here. KVM_REQ_RELOAD_PMU should
already be discarding + recomputing perf events based on the state of
the vPMU. What's the problem?

Thanks,
Oliver

> Assisted-by: Codex:gpt-6-astra
> Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> ---
>  arch/arm64/kvm/pmu-emul.c | 14 ++++++++++++++
>  arch/arm64/kvm/reset.c    |  3 +++
>  arch/arm64/kvm/sys_regs.c |  3 ---
>  include/kvm/arm_pmu.h     |  2 ++
>  4 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index a5ccb6ae44d5..14fcdbdb4587 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -258,6 +258,20 @@ void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu)
>  		pmu->pmc[i].idx = i;
>  }
>  
> +/**
> + * kvm_pmu_vcpu_reset - reset pmu state for cpu
> + * @vcpu: The vcpu pointer
> + *
> + */
> +void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
> +{
> +	unsigned long mask = kvm_pmu_implemented_counter_mask(vcpu);
> +	int i;
> +
> +	for_each_set_bit(i, &mask, 32)
> +		kvm_pmu_stop_counter(kvm_vcpu_idx_to_pmc(vcpu, i));
> +}
> +
>  /**
>   * kvm_pmu_vcpu_destroy - free perf event of PMU for cpu
>   * @vcpu: The vcpu pointer
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 10eb7249aa9e..adcb460a5287 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -185,6 +185,9 @@ void kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  	vcpu->arch.reset_state.reset = false;
>  	spin_unlock(&vcpu->arch.mp_state_lock);
>  
> +	/* Reset PMU outside of the non-preemptible section */
> +	kvm_pmu_vcpu_reset(vcpu);
> +
>  	preempt_disable();
>  	loaded = (vcpu->cpu != -1);
>  	if (loaded)
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1481dd5c99a8..75624725adf1 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -5388,9 +5388,6 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
>  	}
>  
>  	set_bit(KVM_ARCH_FLAG_ID_REGS_INITIALIZED, &kvm->arch.flags);
> -
> -	if (kvm_vcpu_has_pmu(vcpu))
> -		kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
>  }
>  
>  /**
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 6b4a118d17ca..51f5e4ca3326 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -48,6 +48,7 @@ u64 kvm_pmu_implemented_counter_mask(struct kvm_vcpu *vcpu);
>  u64 kvm_pmu_accessible_counter_mask(struct kvm_vcpu *vcpu);
>  u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1);
>  void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu);
> +void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu);
>  void kvm_pmu_vcpu_destroy(struct kvm_vcpu *vcpu);
>  void kvm_pmu_reprogram_counter_mask(struct kvm_vcpu *vcpu, u64 val);
>  void kvm_pmu_flush_hwstate(struct kvm_vcpu *vcpu);
> @@ -125,6 +126,7 @@ static inline u64 kvm_pmu_accessible_counter_mask(struct kvm_vcpu *vcpu)
>  	return 0;
>  }
>  static inline void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu) {}
> +static inline void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_pmu_vcpu_destroy(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_pmu_reprogram_counter_mask(struct kvm_vcpu *vcpu, u64 val) {}
>  static inline void kvm_pmu_flush_hwstate(struct kvm_vcpu *vcpu) {}
> 
> -- 
> 2.55.0
>