[PATCH v6 38/43] arm64: RME: Configure max SVE vector length for a Realm

[Gavin Shan]

On 12/13/24 1:56 AM, Steven Price wrote:
> From: Jean-Philippe Brucker <jean-philippe at linaro.org>
> 
> Obtain the max vector length configured by userspace on the vCPUs, and
> write it into the Realm parameters. By default the vCPU is configured
> with the max vector length reported by RMM, and userspace can reduce it
> with a write to KVM_REG_ARM64_SVE_VLS.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
> Signed-off-by: Steven Price <steven.price at arm.com>
> ---
>   arch/arm64/kvm/guest.c |  3 ++-
>   arch/arm64/kvm/rme.c   | 42 ++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 429c8f10b76a..5562029368c5 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -363,7 +363,7 @@ static int set_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>   	if (!vcpu_has_sve(vcpu))
>   		return -ENOENT;
>   
> -	if (kvm_arm_vcpu_sve_finalized(vcpu))
> +	if (kvm_arm_vcpu_sve_finalized(vcpu) || kvm_realm_is_created(vcpu->kvm))
>   		return -EPERM; /* too late! */
>   
>   	if (WARN_ON(vcpu->arch.sve_state))
> @@ -825,6 +825,7 @@ static bool validate_realm_set_reg(struct kvm_vcpu *vcpu,
>   		switch (reg->id) {
>   		case KVM_REG_ARM_PMCR_EL0:
>   		case KVM_REG_ARM_ID_AA64DFR0_EL1:
> +		case KVM_REG_ARM64_SVE_VLS:
>   			return true;
>   		}
>   	}
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index 39dbc19e4a42..3116ecee37a8 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -297,6 +297,44 @@ static void realm_unmap_shared_range(struct kvm *kvm,
>   	}
>   }
>   
> +static int realm_init_sve_param(struct kvm *kvm, struct realm_params *params)
> +{
> +	int ret = 0;
> +	unsigned long i;
> +	struct kvm_vcpu *vcpu;
> +	int max_vl, realm_max_vl = -1;
> +

I would suggest to rename 'max_vl' and 'realm_max_vl' to 'vl' and 'last_vl'
since we're not looking for the maximal VLs. Instead, we're making sure the
VLs on all vCPUs are equal.

> +	/*
> +	 * Get the preferred SVE configuration, set by userspace with the
> +	 * KVM_ARM_VCPU_SVE feature and KVM_REG_ARM64_SVE_VLS pseudo-register.
> +	 */
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		mutex_lock(&vcpu->mutex);
> +		if (vcpu_has_sve(vcpu)) {
> +			if (!kvm_arm_vcpu_sve_finalized(vcpu))
> +				ret = -EINVAL;
> +			max_vl = vcpu->arch.sve_max_vl;
> +		} else {
> +			max_vl = 0;
> +		}
> +		mutex_unlock(&vcpu->mutex);
> +		if (ret)
> +			return ret;
> +
> +		/* We need all vCPUs to have the same SVE config */
> +		if (realm_max_vl >= 0 && realm_max_vl != max_vl)
> +			return -EINVAL;
> +
> +		realm_max_vl = max_vl;
> +	}
> +
> +	if (realm_max_vl > 0) {
> +		params->sve_vl = sve_vq_from_vl(realm_max_vl) - 1;
> +		params->flags |= RMI_REALM_PARAM_FLAG_SVE;
> +	}
> +	return 0;
> +}
> +
>   static int realm_create_rd(struct kvm *kvm)
>   {
>   	struct realm *realm = &kvm->arch.realm;
> @@ -344,6 +382,10 @@ static int realm_create_rd(struct kvm *kvm)
>   		params->flags |= RMI_REALM_PARAM_FLAG_PMU;
>   	}
>   
> +	r = realm_init_sve_param(kvm, params);
> +	if (r)
> +		goto out_undelegate_tables;
> +
>   	params_phys = virt_to_phys(params);
>   
>   	if (rmi_realm_create(rd_phys, params_phys)) {

Thanks,
Gavin