Re: [PATCH v9 07/43] arm64: RME: ioctls to create and configure realms

[Steven Price]

On 23/06/2025 14:17, zhuangyiwei wrote:
> Hi Steven
> 
> On 2025/6/11 18:48, Steven Price wrote:
>> Add the KVM_CAP_ARM_RME_CREATE_RD ioctl to create a realm. This involves
>> delegating pages to the RMM to hold the Realm Descriptor (RD) and for
>> the base level of the Realm Translation Tables (RTT). A VMID also need
>> to be picked, since the RMM has a separate VMID address space a
>> dedicated allocator is added for this purpose.
>>
>> KVM_CAP_ARM_RME_CONFIG_REALM is provided to allow configuring the realm
>> before it is created. Configuration options can be classified as:
>>
>>   1. Parameters specific to the Realm stage2 (e.g. IPA Size, vmid, stage2
>>      entry level, entry level RTTs, number of RTTs in start level, LPA2)
>>      Most of these are not measured by RMM and comes from KVM book
>>      keeping.
>>
>>   2. Parameters controlling "Arm Architecture features for the VM". (e.g.
>>      SVE VL, PMU counters, number of HW BRPs/WPs), configured by the VMM
>>      using the "user ID register write" mechanism. These will be
>>      supported in the later patches.
>>
>>   3. Parameters are not part of the core Arm architecture but defined
>>      by the RMM spec (e.g. Hash algorithm for measurement,
>>      Personalisation value). These are programmed via
>>      KVM_CAP_ARM_RME_CONFIG_REALM.
>>
>> For the IPA size there is the possibility that the RMM supports a
>> different size to the IPA size supported by KVM for normal guests. At
>> the moment the 'normal limit' is exposed by KVM_CAP_ARM_VM_IPA_SIZE and
>> the IPA size is configured by the bottom bits of vm_type in
>> KVM_CREATE_VM. This means that it isn't easy for the VMM to discover
>> what IPA sizes are supported for Realm guests. Since the IPA is part of
>> the measurement of the realm guest the current expectation is that the
>> VMM will be required to pick the IPA size demanded by attestation and
>> therefore simply failing if this isn't available is fine. An option
>> would be to expose a new capability ioctl to obtain the RMM's maximum
>> IPA size if this is needed in the future.
>>
>> Co-developed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>> Signed-off-by: Steven Price <steven.price@xxxxxxx>
>> Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
[...]
>> +static int realm_create_rd(struct kvm *kvm)
>> +{
>> +    struct realm *realm = &kvm->arch.realm;
>> +    struct realm_params *params = realm->params;
>> +    void *rd = NULL;
>> +    phys_addr_t rd_phys, params_phys;
>> +    size_t pgd_size = kvm_pgtable_stage2_pgd_size(kvm->arch.mmu.vtcr);
>> +    int i, r;
>> +    int rtt_num_start;
>> +
>> +    realm->ia_bits = VTCR_EL2_IPA(kvm->arch.mmu.vtcr);
>> +    rtt_num_start = realm_num_root_rtts(realm);
>> +
>> +    if (WARN_ON(realm->rd || !realm->params))
>> +        return -EEXIST;
>> +
>> +    if (pgd_size / RMM_PAGE_SIZE < rtt_num_start)
>> +        return -EINVAL;
>> +
>> +    rd = (void *)__get_free_page(GFP_KERNEL);
>> +    if (!rd)
>> +        return -ENOMEM;
>> +
>> +    rd_phys = virt_to_phys(rd);
>> +    if (rmi_granule_delegate(rd_phys)) {
>> +        r = -ENXIO;
>> +        goto free_rd;
>> +    }
>> +
>> +    for (i = 0; i < pgd_size; i += RMM_PAGE_SIZE) {
>> +        phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i;
>> +
>> +        if (rmi_granule_delegate(pgd_phys)) {
>> +            r = -ENXIO;
>> +            goto out_undelegate_tables;
>> +        }
>> +    }
>> +
>> +    params->s2sz = VTCR_EL2_IPA(kvm->arch.mmu.vtcr);
>> +    params->rtt_level_start = get_start_level(realm);
>> +    params->rtt_num_start = rtt_num_start;
>> +    params->rtt_base = kvm->arch.mmu.pgd_phys;
>> +    params->vmid = realm->vmid;
>> +
>> +    params_phys = virt_to_phys(params);
>> +
>> +    if (rmi_realm_create(rd_phys, params_phys)) {
>> +        r = -ENXIO;
>> +        goto out_undelegate_tables;
>> +    }
>> +
>> +    if (WARN_ON(rmi_rec_aux_count(rd_phys, &realm->num_aux))) {
>> +        WARN_ON(rmi_realm_destroy(rd_phys));
> 
> Since r has not been initialized, "goto out_undelegate_tables" leads to
> 
> return unknown value.

Good spot! That should have a "r = -ENXIO" line in there.

Thanks for the review,
Steve