linux-kernel - Re: [PATCH v8 06/13] KVM: arm64: Sanitize PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR} before first run

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Message-ID: <86y1ft4ijm.wl-maz@kernel.org>
Date:   Mon, 23 Oct 2023 13:42:05 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Shaoqin Huang <shahuang@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 06/13] KVM: arm64: Sanitize PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR} before first run

On Fri, 20 Oct 2023 22:40:46 +0100,
Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> 
> For unimplemented counters, the registers PM{C,I}NTEN{SET,CLR}
> and PMOVS{SET,CLR} are expected to have the corresponding bits RAZ.
> Hence to ensure correct KVM's PMU emulation, mask out the bits in
> these registers for these unimplemented counters before the first
> vCPU run.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> ---
>  arch/arm64/kvm/arm.c      |  2 +-
>  arch/arm64/kvm/pmu-emul.c | 11 +++++++++++
>  include/kvm/arm_pmu.h     |  2 ++
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e3074a9e23a8b..3c0bb80483fb1 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -857,7 +857,7 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
>  		}
>  
>  		if (kvm_check_request(KVM_REQ_RELOAD_PMU, vcpu))
> -			kvm_pmu_handle_pmcr(vcpu, kvm_vcpu_read_pmcr(vcpu));
> +			kvm_vcpu_handle_request_reload_pmu(vcpu);

Please rename this to kvm_vcpu_reload_pmu(). That's long enough. But
see below.

>
>  		if (kvm_check_request(KVM_REQ_RESYNC_PMU_EL0, vcpu))
>  			kvm_vcpu_pmu_restore_guest(vcpu);
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index 9e24581206c24..31e4933293b76 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -788,6 +788,17 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
>  	return val & mask;
>  }
>  
> +void kvm_vcpu_handle_request_reload_pmu(struct kvm_vcpu *vcpu)
> +{
> +	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
> +
> +	kvm_pmu_handle_pmcr(vcpu, kvm_vcpu_read_pmcr(vcpu));
> +
> +	__vcpu_sys_reg(vcpu, PMOVSSET_EL0) &= mask;
> +	__vcpu_sys_reg(vcpu, PMINTENSET_EL1) &= mask;
> +	__vcpu_sys_reg(vcpu, PMCNTENSET_EL0) &= mask;
> +}

Why is this done on a vcpu request? Why can't it be done upfront, when
we're requesting the reload? Or when assigning the PMU? Or when
setting PMCR_EL0?

	M.

-- 
Without deviation from the norm, progress is not possible.