Re: [PATCH v2] KVM: arm/arm64: Introduce kvm_pmu_vcpu_init() to setup PMU counter idx

[Julien Thierry]

Hi Zenghui,

On 18/07/2019 09:15, Zenghui Yu wrote:
> We use "pmc->idx" and the "chained" bitmap to determine if the pmc is
> chained, in kvm_pmu_pmc_is_chained().  But idx might be uninitialized
> (and random) when we doing this decision, through a KVM_ARM_VCPU_INIT
> ioctl -> kvm_pmu_vcpu_reset(). And the test_bit() against this random
> idx will potentially hit a KASAN BUG [1].
> 
> In general, idx is the static property of a PMU counter that is not
> expected to be modified across resets, as suggested by Julien.  It
> looks more reasonable if we can setup the PMU counter idx for a vcpu
> in its creation time. Introduce a new function - kvm_pmu_vcpu_init()
> for this basic setup. Oh, and the KASAN BUG will get fixed this way.
> 
> [1] https://www.spinics.net/lists/kvm-arm/msg36700.html
> 
> Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
> Suggested-by: Andrew Murray <andrew.murray@xxxxxxx>
> Suggested-by: Julien Thierry <julien.thierry@xxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> ---
> 
> Changes since v1:
>  - Introduce kvm_pmu_vcpu_init() in vcpu's creation time, move the
>    assignment of pmc->idx into it.
>  - Thus change the subject. The old one is "KVM: arm/arm64: Assign
>    pmc->idx before kvm_pmu_stop_counter()".
> 
> Julien, I haven't collected your Acked-by into this version. If you're
> still happy with the change, please Ack again. Thanks!
> 

Thanks for making the change. This looks good to me:

Acked-by: Julien Thierry <julien.thierry@xxxxxxx>

Thanks,

Julien

>  include/kvm/arm_pmu.h |  2 ++
>  virt/kvm/arm/arm.c    |  2 ++
>  virt/kvm/arm/pmu.c    | 18 +++++++++++++++---
>  3 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 16c769a..6db0304 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -34,6 +34,7 @@ struct kvm_pmu {
>  u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx);
>  void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val);
>  u64 kvm_pmu_valid_counter_mask(struct kvm_vcpu *vcpu);
> +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_disable_counter_mask(struct kvm_vcpu *vcpu, u64 val);
> @@ -71,6 +72,7 @@ static inline u64 kvm_pmu_valid_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_disable_counter_mask(struct kvm_vcpu *vcpu, u64 val) {}
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index f645c0f..c704fa6 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -340,6 +340,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>  	/* Set up the timer */
>  	kvm_timer_vcpu_init(vcpu);
>  
> +	kvm_pmu_vcpu_init(vcpu);
> +
>  	kvm_arm_reset_debug_ptr(vcpu);
>  
>  	return kvm_vgic_vcpu_init(vcpu);
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 3dd8238..362a018 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -215,6 +215,20 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
>  }
>  
>  /**
> + * kvm_pmu_vcpu_init - assign pmu counter idx for cpu
> + * @vcpu: The vcpu pointer
> + *
> + */
> +void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu)
> +{
> +	int i;
> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> +
> +	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
> +		pmu->pmc[i].idx = i;
> +}
> +
> +/**
>   * kvm_pmu_vcpu_reset - reset pmu state for cpu
>   * @vcpu: The vcpu pointer
>   *
> @@ -224,10 +238,8 @@ void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
>  	int i;
>  	struct kvm_pmu *pmu = &vcpu->arch.pmu;
>  
> -	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) {
> +	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
>  		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
> -		pmu->pmc[i].idx = i;
> -	}
>  
>  	bitmap_zero(vcpu->arch.pmu.chained, ARMV8_PMU_MAX_COUNTER_PAIRS);
>  }
> 

-- 
Julien Thierry