[PATCH v14 19/44] arm64: RMI: Allocate/free RECs to match vCPUs
Steven Price
steven.price at arm.com
Fri Jun 5 08:02:12 PDT 2026
On 26/05/2026 23:39, Wei-Lin Chang wrote:
> Hi,
>
> On Wed, May 13, 2026 at 02:17:27PM +0100, Steven Price wrote:
>> The RMM maintains a data structure known as the Realm Execution Context
>> (or REC). It is similar to struct kvm_vcpu and tracks the state of the
>> virtual CPUs. KVM must delegate memory and request the structures are
>> created when vCPUs are created, and suitably tear down on destruction.
>>
>> RECs may require additional pages (e.g. for storing larger register
>> state for SVE). The RMM can request extra pages for this purpose using
>> the Stateful RMI Operations (SRO) functionality to request pages during
>> REC creation. These pages are then passed back to the host from the RMM
>> ('reclaimed') when the REC is destroyed. The kernel tracking object
>> (struct rmi_sro_state) is stored in the realm_rec structure to avoid
>> memory allocation during the destruction path.
>>
>> Note that only some of register state for the REC can be set by KVM, the
>> rest is defined by the RMM (zeroed). The register state then cannot be
>> changed by KVM after the REC is created (except when the guest
>> explicitly requests this e.g. by performing a PSCI call).
>>
>> Signed-off-by: Steven Price <steven.price at arm.com>
>> ---
>> Changes since v13:
>> * Support SRO for REC creation/destruction instead of auxiliary
>> granules.
>> Changes since v12:
>> * Use the new range-based delegation RMI.
>> Changes since v11:
>> * Remove the KVM_ARM_VCPU_REC feature. User space no longer needs to
>> configure each VCPU separately, RECs are created on the first VCPU
>> run of the guest.
>> Changes since v9:
>> * Size the aux_pages array according to the PAGE_SIZE of the host.
>> Changes since v7:
>> * Add comment explaining the aux_pages array.
>> * Rename "undeleted_failed" variable to "should_free" to avoid a
>> confusing double negative.
>> Changes since v6:
>> * Avoid reporting the KVM_ARM_VCPU_REC feature if the guest isn't a
>> realm guest.
>> * Support host page size being larger than RMM's granule size when
>> allocating/freeing aux granules.
>> Changes since v5:
>> * Separate the concept of vcpu_is_rec() and
>> kvm_arm_vcpu_rec_finalized() by using the KVM_ARM_VCPU_REC feature as
>> the indication that the VCPU is a REC.
>> Changes since v2:
>> * Free rec->run earlier in kvm_destroy_realm() and adapt to previous patches.
>> ---
>> arch/arm64/include/asm/kvm_emulate.h | 2 +-
>> arch/arm64/include/asm/kvm_host.h | 3 +
>> arch/arm64/include/asm/kvm_rmi.h | 17 +++++
>> arch/arm64/kvm/arm.c | 6 ++
>> arch/arm64/kvm/reset.c | 1 +
>> arch/arm64/kvm/rmi.c | 105 +++++++++++++++++++++++++++
>> 6 files changed, 133 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index 82fd777bd9bb..2e69fe494716 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -714,7 +714,7 @@ static inline bool kvm_realm_is_created(struct kvm *kvm)
>>
>> static inline bool vcpu_is_rec(const struct kvm_vcpu *vcpu)
>> {
>> - return false;
>> + return kvm_is_realm(vcpu->kvm);
>> }
>>
>> #endif /* __ARM64_KVM_EMULATE_H__ */
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 3512696ed506..39b5de03d0fe 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -969,6 +969,9 @@ struct kvm_vcpu_arch {
>>
>> /* Hyp-readable copy of kvm_vcpu::pid */
>> pid_t pid;
>> +
>> + /* Realm meta data */
>> + struct realm_rec rec;
>> };
>>
>> /*
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
>> index 8bd743093ccf..d99bf4fc3c39 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -59,6 +59,22 @@ struct realm {
>> unsigned int ia_bits;
>> };
>>
>> +/**
>> + * struct realm_rec - Additional per VCPU data for a Realm
>> + *
>> + * @mpidr: MPIDR (Multiprocessor Affinity Register) value to identify this VCPU
>> + * @rec_page: Kernel VA of the RMM's private page for this REC
>> + * @aux_pages: Additional pages private to the RMM for this REC
>> + * @run: Kernel VA of the RmiRecRun structure shared with the RMM
>> + * @sro: A preallocated SRO state context
>> + */
>> +struct realm_rec {
>> + unsigned long mpidr;
>> + void *rec_page;
>> + struct rec_run *run;
>> + struct rmi_sro_state *sro;
>> +};
>> +
>> void kvm_init_rmi(void);
>> u32 kvm_realm_ipa_limit(void);
>>
>> @@ -66,6 +82,7 @@ int kvm_init_realm(struct kvm *kvm);
>> int kvm_activate_realm(struct kvm *kvm);
>> void kvm_destroy_realm(struct kvm *kvm);
>> void kvm_realm_destroy_rtts(struct kvm *kvm);
>> +void kvm_destroy_rec(struct kvm_vcpu *vcpu);
>>
>> static inline bool kvm_realm_is_private_address(struct realm *realm,
>> unsigned long addr)
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index eb2b61fe1f0a..93d34762db91 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -586,6 +586,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>> /* Force users to call KVM_ARM_VCPU_INIT */
>> vcpu_clear_flag(vcpu, VCPU_INITIALIZED);
>>
>> + vcpu->arch.rec.mpidr = INVALID_HWID;
>> +
>> vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
>>
>> /* Set up the timer */
>> @@ -1651,6 +1653,10 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>> if (test_bit(KVM_ARM_VCPU_HAS_EL2, &features))
>> return -EINVAL;
>>
>> + /* Realms are incompatible with AArch32 */
>> + if (vcpu_is_rec(vcpu))
>> + return -EINVAL;
>> +
>> return 0;
>> }
>>
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index b963fd975aac..c18cdca7d125 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -161,6 +161,7 @@ void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu)
>> free_page((unsigned long)vcpu->arch.ctxt.vncr_array);
>> kfree(vcpu->arch.vncr_tlb);
>> kfree(vcpu->arch.ccsidr);
>> + kvm_destroy_rec(vcpu);
>> }
>>
>> static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> index 849111817af7..353a5ca45e78 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -173,9 +173,108 @@ static int realm_ensure_created(struct kvm *kvm)
>> return -ENXIO;
>> }
>>
>> +static int kvm_create_rec(struct kvm_vcpu *vcpu)
>> +{
>> + struct user_pt_regs *vcpu_regs = vcpu_gp_regs(vcpu);
>> + unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
>> + struct realm *realm = &vcpu->kvm->arch.realm;
>> + struct realm_rec *rec = &vcpu->arch.rec;
>> + unsigned long rec_page_phys;
>> + struct rec_params *params;
>> + int r, i;
>> +
>> + if (rec->run)
>> + return -EBUSY;
>> +
>> + /*
>> + * The RMM will report PSCI v1.0 to Realms and the KVM_ARM_VCPU_PSCI_0_2
>> + * flag covers v0.2 and onwards.
>> + */
>> + if (!vcpu_has_feature(vcpu, KVM_ARM_VCPU_PSCI_0_2))
>> + return -EINVAL;
>> +
>> + BUILD_BUG_ON(sizeof(*params) > PAGE_SIZE);
>> + BUILD_BUG_ON(sizeof(*rec->run) > PAGE_SIZE);
>> +
>> + params = (struct rec_params *)get_zeroed_page(GFP_KERNEL);
>> + rec->rec_page = (void *)__get_free_page(GFP_KERNEL);
>> + rec->run = (void *)get_zeroed_page(GFP_KERNEL);
>
> Should this be cast to (struct rec_run *) ?
Yes it probably should - I'll update. Although IMHO get_zeroed_page()
should really return void * - but I know that would be a contentious change.
Thanks,
Steve
>> + rec->sro = kmalloc_obj(*rec->sro);
>> + if (!params || !rec->rec_page || !rec->run || !rec->sro) {
>> + r = -ENOMEM;
>> + goto out_free_pages;
>> + }
>> +
>> + for (i = 0; i < ARRAY_SIZE(params->gprs); i++)
>> + params->gprs[i] = vcpu_regs->regs[i];
>> +
>> + params->pc = vcpu_regs->pc;
>> +
>> + if (vcpu->vcpu_id == 0)
>> + params->flags |= REC_PARAMS_FLAG_RUNNABLE;
>> +
>> + rec_page_phys = virt_to_phys(rec->rec_page);
>> +
>> + if (rmi_delegate_page(rec_page_phys)) {
>> + r = -ENXIO;
>> + goto out_free_pages;
>> + }
>> +
>> + params->mpidr = mpidr;
>> +
>> + if (rmi_rec_create(virt_to_phys(realm->rd), rec_page_phys,
>> + virt_to_phys(params), rec->sro)) {
>> + r = -ENXIO;
>> + goto out_undelegate_rmm_rec;
>> + }
>> +
>> + rec->mpidr = mpidr;
>> +
>> + free_page((unsigned long)params);
>> + return 0;
>> +
>> +out_undelegate_rmm_rec:
>> + if (WARN_ON(rmi_undelegate_page(rec_page_phys)))
>> + rec->rec_page = NULL;
>> +out_free_pages:
>> + free_page((unsigned long)rec->run);
>> + free_page((unsigned long)rec->rec_page);
>> + free_page((unsigned long)params);
>> + kfree(rec->sro);
>> + rec->run = NULL;
>> + return r;
>> +}
>> +
>
> [...]
>
> Thanks,
> Wei-Lin Chang
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