Re: [RFC PATCH v2 3/5] Add APIs to get/set MTE tags

[Juan Quintela]

Haibo Xu <haibo.xu@linaro.org> wrote:
> MTE spec provide instructions to retrieve the memory tags:
> (1) LDG, at 16 bytes granularity, and available in both user
>     and kernel space;
> (2) LDGM, at 256 bytes granularity in maximum, and only
>     available in kernel space
>
> To improve the performance, KVM has exposed the LDGM capability
> to user space by providing a new APIs. This patch is just a
> wrapper for the KVM APIs.
>
> Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
> ---
>  target/arm/kvm64.c   | 24 ++++++++++++++++++++++++
>  target/arm/kvm_arm.h |  2 ++
>  2 files changed, 26 insertions(+)
>
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 73a191f8e1..3157025316 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -1606,3 +1606,27 @@ bool kvm_arm_verify_ext_dabt_pending(CPUState *cs)
>      }
>      return false;
>  }
> +
> +int kvm_arm_mte_get_tags(uint64_t ipa, uint64_t len, uint8_t *buf)
> +{
> +    struct kvm_arm_copy_mte_tags args = {
> +        .guest_ipa = ipa,
> +        .length = len,
> +        .addr = buf,
> +        .flags = KVM_ARM_TAGS_FROM_GUEST,
> +    };
> +
> +    return kvm_vm_ioctl(kvm_state, KVM_ARM_MTE_COPY_TAGS, &args);

Just a question, how fast/slow are this calls?

My understanding is that we are making a kvm call for each page that we
want to migrate, right?

Each time that we want to send it.

Later, Juan.


> +}
> +
> +int kvm_arm_mte_set_tags(uint64_t ipa, uint64_t len, uint8_t *buf)
> +{
> +    struct kvm_arm_copy_mte_tags args = {
> +        .guest_ipa = ipa,
> +        .length = len,
> +        .addr = buf,
> +        .flags = KVM_ARM_TAGS_TO_GUEST,
> +    };
> +
> +    return kvm_vm_ioctl(kvm_state, KVM_ARM_MTE_COPY_TAGS, &args);
> +}
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index 34f8daa377..bbb833d6c6 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -360,6 +360,8 @@ int kvm_arm_vgic_probe(void);
>  
>  void kvm_arm_pmu_set_irq(CPUState *cs, int irq);
>  void kvm_arm_pmu_init(CPUState *cs);
> +int kvm_arm_mte_get_tags(uint64_t ipa, uint64_t len, uint8_t *buf);
> +int kvm_arm_mte_set_tags(uint64_t ipa, uint64_t len, uint8_t *buf);
>  
>  /**
>   * kvm_arm_pvtime_init: