Re: [PATCH v13 12/48] arm64: RMI: Basic infrastructure for creating a realm.

Steven Price
2026-03-20T16:07:50Z

On 19/03/2026 17:17, Wei-Lin Chang wrote:
> On Wed, Mar 18, 2026 at 03:53:36PM +0000, Steven Price wrote:
>> Introduce the skeleton functions for creating and destroying a realm.
>> The IPA size requested is checked against what the RMM supports.
>>
>> The actual work of constructing the realm will be added in future
>> patches.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>> Changes since v12:
>> * Drop the RMM_PAGE_{SHIFT,SIZE} defines - the RMM is now configured to
>> be the same as the host's page size.
>> * Rework delegate/undelegate functions to use the new RMI range based
>> operations.
>> Changes since v11:
>> * Major rework to drop the realm configuration and make the
>> construction of realms implicit rather than driven by the VMM
>> directly.
>> * The code to create RDs, handle VMIDs etc is moved to later patches.
>> Changes since v10:
>> * Rename from RME to RMI.
>> * Move the stage2 cleanup to a later patch.
>> Changes since v9:
>> * Avoid walking the stage 2 page tables when destroying the realm -
>> the real ones are not accessible to the non-secure world, and the RMM
>> may leave junk in the physical pages when returning them.
>> * Fix an error path in realm_create_rd() to actually return an error value.
>> Changes since v8:
>> * Fix free_delegated_granule() to not call kvm_account_pgtable_pages();
>> a separate wrapper will be introduced in a later patch to deal with
>> RTTs.
>> * Minor code cleanups following review.
>> Changes since v7:
>> * Minor code cleanup following Gavin's review.
>> Changes since v6:
>> * Separate RMM RTT calculations from host PAGE_SIZE. This allows the
>> host page size to be larger than 4k while still communicating with an
>> RMM which uses 4k granules.
>> Changes since v5:
>> * Introduce free_delegated_granule() to replace many
>> undelegate/free_page() instances and centralise the comment on
>> leaking when the undelegate fails.
>> * Several other minor improvements suggested by reviews - thanks for
>> the feedback!
>> Changes since v2:
>> * Improved commit description.
>> * Improved return failures for rmi_check_version().
>> * Clear contents of PGD after it has been undelegated in case the RMM
>> left stale data.
>> * Minor changes to reflect changes in previous patches.
>> ---
>> arch/arm64/include/asm/kvm_emulate.h | 5 ++
>> arch/arm64/include/asm/kvm_rmi.h | 16 +++++
>> arch/arm64/kvm/arm.c | 12 ++++
>> arch/arm64/kvm/mmu.c | 11 +++-
>> arch/arm64/kvm/rmi.c | 88 ++++++++++++++++++++++++++++
>> 5 files changed, 129 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index f38b50151ce8..39310d9b4e16 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -701,6 +701,11 @@ static inline enum realm_state kvm_realm_state(struct kvm *kvm)
>> return READ_ONCE(kvm->arch.realm.state);
>> }
>>
>> +static inline bool kvm_realm_is_created(struct kvm *kvm)
>> +{
>> + return kvm_is_realm(kvm) && kvm_realm_state(kvm) != REALM_STATE_NONE;
>> +}
>> +
>> static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
>> {
>> return false;
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
>> index 3506f50b05cd..0ada525af18f 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -6,6 +6,8 @@
>> #ifndef __ASM_KVM_RMI_H
>> #define __ASM_KVM_RMI_H
>>
>> +#include <asm/rmi_smc.h>
>> +
>> /**
>> * enum realm_state - State of a Realm
>> */
>> @@ -46,11 +48,25 @@ enum realm_state {
>> * struct realm - Additional per VM data for a Realm
>> *
>> * @state: The lifetime state machine for the realm
>> + * @rd: Kernel mapping of the Realm Descriptor (RD)
>> + * @params: Parameters for the RMI_REALM_CREATE command
>> + * @num_aux: The number of auxiliary pages required by the RMM
>> + * @ia_bits: Number of valid Input Address bits in the IPA
>> */
>> struct realm {
>> enum realm_state state;
>> +
>> + void *rd;
>> + struct realm_params *params;
>> +
>> + unsigned long num_aux;
>> + unsigned int ia_bits;
>> };
>>
>> void kvm_init_rmi(void);
>> +u32 kvm_realm_ipa_limit(void);
>> +
>> +int kvm_init_realm_vm(struct kvm *kvm);
>> +void kvm_destroy_realm(struct kvm *kvm);
>
> Hi,
>
> Sorry I missed one nit: perhaps call this kvm_init_realm()? So these two
> look like a pair. There are also no realm_vm in other function names.

Makes sense, thanks for the suggestion.

Thanks,
Steve

> Thanks,
> Wei-Lin Chang
>
>>
>> #endif /* __ASM_KVM_RMI_H */
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 274d7866efdc..9b17bdfaf0c2 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -253,6 +253,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>
>> bitmap_zero(kvm->arch.vcpu_features, KVM_VCPU_MAX_FEATURES);
>>
>> + /* Initialise the realm bits after the generic bits are enabled */
>> + if (kvm_is_realm(kvm)) {
>> + ret = kvm_init_realm_vm(kvm);
>> + if (ret)
>> + goto err_free_cpumask;
>> + }
>> +
>> return 0;
>>
>> err_free_cpumask:
>> @@ -312,6 +319,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>> kvm_unshare_hyp(kvm, kvm + 1);
>>
>> kvm_arm_teardown_hypercalls(kvm);
>> + if (kvm_is_realm(kvm))
>> + kvm_destroy_realm(kvm);
>> }
>>
>> static bool kvm_has_full_ptr_auth(void)
>> @@ -473,6 +482,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> else
>> r = kvm_supports_cacheable_pfnmap();
>> break;
>> + case KVM_CAP_ARM_RMI:
>> + r = static_key_enabled(&kvm_rmi_is_available);
>> + break;
>>
>> default:
>> r = 0;
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 070a01e53fcb..d6094b60c4ce 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -872,12 +872,16 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
>> .icache_inval_pou = invalidate_icache_guest_page,
>> };
>>
>> -static int kvm_init_ipa_range(struct kvm_s2_mmu *mmu, unsigned long type)
>> +static int kvm_init_ipa_range(struct kvm *kvm,
>> + struct kvm_s2_mmu *mmu, unsigned long type)
>> {
>> u32 kvm_ipa_limit = get_kvm_ipa_limit();
>> u64 mmfr0, mmfr1;
>> u32 phys_shift;
>>
>> + if (kvm_is_realm(kvm))
>> + kvm_ipa_limit = kvm_realm_ipa_limit();
>> +
>> if (type & ~KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
>> return -EINVAL;
>>
>> @@ -974,7 +978,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
>> return -EINVAL;
>> }
>>
>> - err = kvm_init_ipa_range(mmu, type);
>> + err = kvm_init_ipa_range(kvm, mmu, type);
>> if (err)
>> return err;
>>
>> @@ -1113,7 +1117,8 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
>> write_unlock(&kvm->mmu_lock);
>>
>> if (pgt) {
>> - kvm_stage2_destroy(pgt);
>> + if (!kvm_is_realm(kvm))
>> + kvm_stage2_destroy(pgt);
>> kfree(pgt);
>> }
>> }
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> index 80aedc85e94a..700b8c935d29 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -6,6 +6,8 @@
>> #include <linux/kvm_host.h>
>> #include <linux/memblock.h>
>>
>> +#include <asm/kvm_emulate.h>
>> +#include <asm/kvm_mmu.h>
>> #include <asm/kvm_pgtable.h>
>> #include <asm/rmi_cmds.h>
>> #include <asm/virt.h>
>> @@ -182,6 +184,92 @@ static int rmi_init_metadata(void)
>> return 0;
>> }
>>
>> +u32 kvm_realm_ipa_limit(void)
>> +{
>> + return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
>> +}
>> +
>> +static int undelegate_range(phys_addr_t phys, unsigned long size)
>> +{
>> + unsigned long ret;
>> + unsigned long top = phys + size;
>> + unsigned long out_top;
>> +
>> + while (phys < top) {
>> + ret = rmi_granule_range_undelegate(phys, top, &out_top);
>> + if (ret == RMI_SUCCESS)
>> + phys = out_top;
>> + else if (ret != RMI_BUSY && ret != RMI_BLOCKED)
>> + return ret;
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int undelegate_page(phys_addr_t phys)
>> +{
>> + return undelegate_range(phys, PAGE_SIZE);
>> +}
>> +
>> +static int free_delegated_page(phys_addr_t phys)
>> +{
>> + if (WARN_ON(undelegate_page(phys))) {
>> + /* Undelegate failed: leak the page */
>> + return -EBUSY;
>> + }
>> +
>> + free_page((unsigned long)phys_to_virt(phys));
>> +
>> + return 0;
>> +}
>> +
>> +void kvm_destroy_realm(struct kvm *kvm)
>> +{
>> + struct realm *realm = &kvm->arch.realm;
>> + size_t pgd_size = kvm_pgtable_stage2_pgd_size(kvm->arch.mmu.vtcr);
>> +
>> + write_lock(&kvm->mmu_lock);
>> + kvm_stage2_unmap_range(&kvm->arch.mmu, 0,
>> + BIT(realm->ia_bits - 1), true);
>> + write_unlock(&kvm->mmu_lock);
>> +
>> + if (realm->params) {
>> + free_page((unsigned long)realm->params);
>> + realm->params = NULL;
>> + }
>> +
>> + if (!kvm_realm_is_created(kvm))
>> + return;
>> +
>> + WRITE_ONCE(realm->state, REALM_STATE_DYING);
>> +
>> + if (realm->rd) {
>> + phys_addr_t rd_phys = virt_to_phys(realm->rd);
>> +
>> + if (WARN_ON(rmi_realm_destroy(rd_phys)))
>> + return;
>> + free_delegated_page(rd_phys);
>> + realm->rd = NULL;
>> + }
>> +
>> + if (WARN_ON(undelegate_range(kvm->arch.mmu.pgd_phys, pgd_size)))
>> + return;
>> +
>> + WRITE_ONCE(realm->state, REALM_STATE_DEAD);
>> +
>> + /* Now that the Realm is destroyed, free the entry level RTTs */
>> + kvm_free_stage2_pgd(&kvm->arch.mmu);
>> +}
>> +
>> +int kvm_init_realm_vm(struct kvm *kvm)
>> +{
>> + kvm->arch.realm.params = (void *)get_zeroed_page(GFP_KERNEL);
>> +
>> + if (!kvm->arch.realm.params)
>> + return -ENOMEM;
>> + return 0;
>> +}
>> +
>> static int rmm_check_features(void)
>> {
>> if (kvm_lpa2_is_enabled() && !rmi_has_feature(RMI_FEATURE_REGISTER_0_LPA2)) {
>> --
>> 2.43.0
>>