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
> Suggested-by: Julien Thierry
> Cc: Marc Zyngier
> Signed-off-by: Zenghui Yu
> ---
>
> 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
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
