Re: [PATCH 06/11] KVM: arm64: CCA: Add basic infrastructure for creating a realm
From: Steven Price
Date: Thu Nov 05 2026 - 11:14:17 EST
On 02/11/2026 23:49, Suzuki K Poulose wrote:
> Hi Steven
>
> On 02/11/2026 14:12, 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@xxxxxxx>
>> ---
>> arch/arm64/include/asm/kvm_rmi.h | 20 ++++++++++++
>> arch/arm64/kvm/arm.c | 9 +++++
>> arch/arm64/kvm/mmu.c | 18 ++++++++--
>> arch/arm64/kvm/rmi.c | 56 ++++++++++++++++++++++++++++++++
>> 4 files changed, 101 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/
>> asm/kvm_rmi.h
>> index 3194daaacf2b..f1a1ed6b91f5 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -6,6 +6,9 @@
>> #ifndef __ASM_KVM_RMI_H
>> #define __ASM_KVM_RMI_H
>> +#include <linux/arm-smccc-rmi.h>
>> +#include <linux/kvm.h>
>> +
>> /**
>> * enum realm_state - State of a Realm
>> *
>> @@ -50,12 +53,29 @@ enum realm_state {
>> /**
>> * struct realm - Additional per VM data for a Realm
>> *
>> + * @rd: Kernel mapping of the RMM-managed Realm Descriptor (RD) granule
>> + * @sro: Preallocated SRO state context for Realm MMU operations
>> * @state: The lifetime state machine for the realm
>> + * @ia_bits: Number of valid Input Address bits in the IPA
>> */
>> struct realm {
>> + void *rd;
>> + /*
>> + * Reused by RTT map/unmap SRO commands. Those commands are only
>> + * issued from Realm stage-2 map/unmap paths while kvm->mmu_lock is
>> + * held for write, including Realm fault handling where
>> + * kvm_fault_lock() takes the write side, so concurrent use is
>> + * serialized.
>> + */
>> + struct rmi_sro_state *sro;
>> enum realm_state state;
>> + unsigned int ia_bits;
>> };
>> void kvm_init_rmi(void);
>> +u32 kvm_rmm_ipa_limit(void);
>> +
>> +int kvm_init_realm(struct kvm *kvm);
>> +void kvm_destroy_realm(struct kvm *kvm);
>> #endif /* __ASM_KVM_RMI_H */
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index c8599fed5902..9a7bbfaf9675 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -303,6 +303,13 @@ 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_vm_is_realm(kvm)) {
>> + ret = kvm_init_realm(kvm);
>> + if (ret)
>> + goto err_uninit_mmu;
>> + }
>> +
>> return 0;
>> err_uninit_mmu:
>> @@ -367,6 +374,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>> kvm_destroy_nested(kvm);
>> kvm_arm_teardown_hypercalls(kvm);
>> + if (kvm_vm_is_realm(kvm))
>> + kvm_destroy_realm(kvm);
>> }
>> static bool kvm_has_full_ptr_auth(void)
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 1301c563d705..b049ea67d9af 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -981,10 +981,14 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
>> static int kvm_init_ipa_range(struct kvm_s2_mmu *mmu, unsigned
>> long type)
>> {
>> + struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
>> u32 kvm_ipa_limit = get_kvm_ipa_limit();
>> u64 mmfr0, mmfr1;
>> u32 phys_shift;
>> + if (kvm_vm_is_realm(kvm))
>> + kvm_ipa_limit = kvm_rmm_ipa_limit();
>> +
>> phys_shift = KVM_VM_TYPE_ARM_IPA_SIZE(type);
>> if (is_protected_kvm_enabled()) {
>> phys_shift = kvm_ipa_limit;
>> @@ -1034,9 +1038,18 @@ static void stage2_destroy_range(struct
>> kvm_pgtable *pgt, phys_addr_t addr,
>> static void kvm_stage2_destroy(struct kvm_pgtable *pgt)
>> {
>> + struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu);
>> unsigned int ia_bits = VTCR_EL2_IPA(pgt->mmu->vtcr);
>> - stage2_destroy_range(pgt, 0, BIT(ia_bits));
>> + /*
>> + * Realm RTTs are inaccessible to the host and may contain stale
>> data
>> + * after the RMM has released them. The non-root RTTs are explicitly
>> + * destroyed through RMI before the RD is destroyed; only the
>> root PGD
>> + * pages remain to be freed here.
>> + */
>> + if (!kvm_vm_is_realm(kvm))
>> + stage2_destroy_range(pgt, 0, BIT(ia_bits));
>> +
>> KVM_PGT_FN(kvm_pgtable_stage2_destroy_pgd)(pgt);
>> }
>
> This looks like a good candidate for another callback for vm_s2_ops ?
> Something like (incomplete functionally, but this should work).
> As a bonus, we can remove two instances of KVM_PGT_FN()
Nice, yes that's an improvement. Thanks for the suggestion.
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 5e9c2919c509..96685c52fb6e 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1048,35 +1048,52 @@ static int kvm_init_ipa_range(struct kvm_s2_mmu
> *mmu, unsigned long type)
> * cond_resched() periodically to prevent hogging the CPU for a long time
> * and schedule something else, if required.
> */
> -static void stage2_destroy_range(struct kvm_pgtable *pgt, phys_addr_t
> addr,
> - phys_addr_t end)
> +static void stage2_destroy_range(struct kvm_pgtable *pgt,
> + void (*pgt_destroy_range_fn)(struct kvm_pgtable *pgt,
> + u64 addr, u64 size))
> {
> + u64 addr = 0;
> + u64 end = BIT(VTCR_EL2_IPA(pgt->mmu->vtcr));
> u64 next;
>
> do {
> next = stage2_range_addr_end(addr, end);
> - KVM_PGT_FN(kvm_pgtable_stage2_destroy_range)(pgt, addr,
> - next - addr);
> + pgt_destroy_range_fn(pgt, addr, next - addr);
> if (next != end)
> cond_resched();
> } while (addr = next, addr != end);
> }
>
> +static void kvm_vm_stage2_destroy(struct kvm_pgtable *pgt)
> +{
> + stage2_destroy_range(pgt, kvm_pgtable_stage2_destroy_range);
> + kvm_pgtable_stage2_destroy_pgd(pgt);
> +}
> +
> +static void pkvm_stage2_destroy(struct kvm_pgtable *pgt)
> +{
> + stage2_destroy_range(pgt, kvm_pgtable_stage2_destroy_range);
> + pkvm_pgtable_stage2_destroy_pgd(pgt);
> +}
> +
> +/*
> +* Realm RTTs are inaccessible to the host and may contain stale data
> +* after the RMM has released them. The non-root RTTs are explicitly
> +* destroyed through RMI before the RD is destroyed; only the root PGD
> +* pages remain to be freed here.
> +*/
> +static void realm_stage2_destroy(struct kvm_pgtable *pgt,
> + u64 start, u64 end)
> +{
> + kvm_pgtable_destroy_pgd(pgt);
> +}
> +
> static void kvm_stage2_destroy(struct kvm_pgtable *pgt)
> {
> struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu);
> unsigned int ia_bits = VTCR_EL2_IPA(pgt->mmu->vtcr);
>
> - /*
> - * Realm RTTs are inaccessible to the host and may contain stale data
> - * after the RMM has released them. The non-root RTTs are explicitly
> - * destroyed through RMI before the RD is destroyed; only the root PGD
> - * pages remain to be freed here.
> - */
> - if (!kvm_vm_is_realm(kvm))
> - stage2_destroy_range(pgt, 0, BIT(ia_bits));
> -
> - KVM_PGT_FN(kvm_pgtable_stage2_destroy_pgd)(pgt);
> + kvm->arch.vm_s2_ops->stage2_destroy(pgt, 0, BIT(ia_bits));
> }
>
>
>
>
>
>> @@ -1084,6 +1097,8 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct
>> kvm_s2_mmu *mmu, unsigned long t
>> return -EINVAL;
>> }
>> + mmu->arch = &kvm->arch;
>> +
>> err = kvm_init_ipa_range(mmu, type);
>> if (err)
>> return err;
>> @@ -1092,7 +1107,6 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct
>> kvm_s2_mmu *mmu, unsigned long t
>> if (!pgt)
>> return -ENOMEM;
>> - mmu->arch = &kvm->arch;
>> err = KVM_PGT_FN(kvm_pgtable_stage2_init)(pgt, mmu,
>> &kvm_s2_mm_ops);
>> if (err)
>> goto out_free_pgtable;
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> index 5b07beff8bc9..45ecbaa467d1 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -6,6 +6,8 @@
>> #include <linux/arm-rmi-cmds.h>
>> #include <linux/kvm_host.h>
>> +#include <asm/kvm_emulate.h>
>> +#include <asm/kvm_mmu.h>
>> #include <asm/kvm_pgtable.h>
>> #include <asm/virt.h>
>> @@ -14,6 +16,60 @@ static bool rmi_has_feature(int reg, unsigned
>> long feature)
>> return !!u64_get_bits(rmi_feat_reg(reg), feature);
>> }
>> +u32 kvm_rmm_ipa_limit(void)
>> +{
>> + return u64_get_bits(rmi_feat_reg(0), RMI_FEATURE_REGISTER_0_S2SZ);
>> +}
>> +
>> +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);
>> +
>> + if (!kvm_realm_is_created(kvm)) {
>> + kfree(realm->sro);
>> + realm->sro = NULL;
>> + return;
>> + }
>
> Do we leak memory of the stage2 PGD if the Realm was never created ?
> Should we have something like on top ?
Sashiko beat you to it - yes I've already got a fix locally for that.
Thanks,
Steve
> @@ -1646,11 +1645,8 @@ void kvm_destroy_realm(struct kvm *kvm)
>
> guard(mutex)(&kvm->arch.config_lock);
>
> - if (!kvm_realm_is_created(kvm)) {
> - kfree(realm->sro);
> - realm->sro = NULL;
> - return;
> - }
> + if (!kvm_realm_is_created(kvm))
> + goto free_pgd;
>
> kvm_set_realm_state(kvm, REALM_STATE_DYING);
>
> @@ -1684,6 +1680,7 @@ void kvm_destroy_realm(struct kvm *kvm)
>
> kvm_set_realm_state(kvm, REALM_STATE_DEAD);
>
> +free_pgd:
> /* Now that the realm is destroyed, free the entry-level RTTs. */
> kvm_free_stage2_pgd(&kvm->arch.mmu);
>
>
> Suzuki
>
>> +
>> + kvm_set_realm_state(kvm, REALM_STATE_DYING);
>> +
>> + if (realm->rd) {
>> + phys_addr_t rd_phys = virt_to_phys(realm->rd);
>> +
>> + if (WARN_ON(rmi_realm_terminate(rd_phys, realm->sro)))
>> + return;
>> +
>> + if (WARN_ON(rmi_realm_destroy(rd_phys, realm->sro)))
>> + return;
>> + rmi_free_delegated_page(rd_phys);
>> + realm->rd = NULL;
>> + }
>> +
>> + if (WARN_ON(rmi_undelegate_range(kvm->arch.mmu.pgd_phys,
>> + pgd_size)))
>> + return;
>> +
>> + kvm_set_realm_state(kvm, REALM_STATE_DEAD);
>> +
>> + /* Now that the realm is destroyed, free the entry-level RTTs. */
>> + kvm_free_stage2_pgd(&kvm->arch.mmu);
>> +
>> + kfree(realm->sro);
>> + realm->sro = NULL;
>> +}
>> +
>> +int kvm_init_realm(struct kvm *kvm)
>> +{
>> + struct realm *realm = &kvm->arch.realm;
>> +
>> + realm->sro = kmalloc_obj(*realm->sro);
>> + if (!realm->sro)
>> + return -ENOMEM;
>> +
>> + return 0;
>> +}
>> +
>> static int rmm_check_features(void)
>> {
>> if (kvm_lpa2_is_enabled() &&
>