linux-kernel - Re: [PATCH v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and PMOVS{SET,CLR} on vCPU reset

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Message-ID: <53546f35-f2cc-4c75-171c-26719550f7df@redhat.com>
Date:   Mon, 16 Oct 2023 21:44:56 +0200
From:   Eric Auger <eauger@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Marc Zyngier <maz@...nel.org>
Cc:     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 v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and
 PMOVS{SET,CLR} on vCPU reset

Hi Raghavendra,

On 10/10/23 01:08, Raghavendra Rao Ananta wrote:
> From: Reiji Watanabe <reijiw@...gle.com>
> 
> On vCPU reset, PMCNTEN{SET,CLR}_EL0, PMINTEN{SET,CLR}_EL1, and
> PMOVS{SET,CLR}_EL1 for a vCPU are reset by reset_pmu_reg().
PMOVS{SET,CLR}_EL0?
> This function clears RAZ bits of those registers corresponding
> to unimplemented event counters on the vCPU, and sets bits
> corresponding to implemented event counters to a predefined
> pseudo UNKNOWN value (some bits are set to 1).
> 
> The function identifies (un)implemented event counters on the
> vCPU based on the PMCR_EL0.N value on the host. Using the host
> value for this would be problematic when KVM supports letting
> userspace set PMCR_EL0.N to a value different from the host value
> (some of the RAZ bits of those registers could end up being set to 1).
> 
> Fix this by clearing the registers so that it can ensure
> that all the RAZ bits are cleared even when the PMCR_EL0.N value
> for the vCPU is different from the host value. Use reset_val() to
> do this instead of fixing reset_pmu_reg(), and remove
> reset_pmu_reg(), as it is no longer used.
do you intend to restore the 'unknown' behavior at some point?

Thanks

Eric
> 
> Signed-off-by: Reiji Watanabe <reijiw@...gle.com>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> ---
>  arch/arm64/kvm/sys_regs.c | 21 +--------------------
>  1 file changed, 1 insertion(+), 20 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 818a52e257ed..3dbb7d276b0e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -717,25 +717,6 @@ static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
>  	return REG_HIDDEN;
>  }
>  
> -static u64 reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> -{
> -	u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
> -
> -	/* No PMU available, any PMU reg may UNDEF... */
> -	if (!kvm_arm_support_pmu_v3())
> -		return 0;
> -
> -	n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
> -	n &= ARMV8_PMU_PMCR_N_MASK;
> -	if (n)
> -		mask |= GENMASK(n - 1, 0);
> -
> -	reset_unknown(vcpu, r);
> -	__vcpu_sys_reg(vcpu, r->reg) &= mask;
> -
> -	return __vcpu_sys_reg(vcpu, r->reg);
> -}
> -
>  static u64 reset_pmevcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>  {
>  	reset_unknown(vcpu, r);
> @@ -1115,7 +1096,7 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>  	  trap_wcr, reset_wcr, 0, 0,  get_wcr, set_wcr }
>  
>  #define PMU_SYS_REG(name)						\
> -	SYS_DESC(SYS_##name), .reset = reset_pmu_reg,			\
> +	SYS_DESC(SYS_##name), .reset = reset_val,			\
>  	.visibility = pmu_visibility
>  
>  /* Macro to expand the PMEVCNTRn_EL0 register */