Re: [PATCH v13 17/48] arm64: RMI: Allocate/free RECs to match vCPUs

Steven Price
2026-03-20T16:27:00Z

On 19/03/2026 18:10, Wei-Lin Chang wrote:
> On Wed, Mar 18, 2026 at 03:53:41PM +0000, 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 must also be supplied with addition pages - auxiliary (or AUX)
>> granules - for storing the larger registers state (e.g. for SVE). The
>> number of AUX granules for a REC depends on the parameters with which
>> the Realm was created - the RMM makes this information available via the
>> RMI_REC_AUX_COUNT call performed after creating the Realm Descriptor (RD).
>>
>> 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@arm.com>
>> ---
>> 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 | 21 +++
>> arch/arm64/kvm/arm.c | 10 +-
>> arch/arm64/kvm/reset.c | 1 +
>> arch/arm64/kvm/rmi.c | 196 +++++++++++++++++++++++++++
>> 6 files changed, 230 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index 39310d9b4e16..d194d91fbc2a 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -708,7 +708,7 @@ static inline bool kvm_realm_is_created(struct kvm *kvm)
>>
>> static inline bool vcpu_is_rec(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 9267a2f2d65b..64304848aad4 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -924,6 +924,9 @@ struct kvm_vcpu_arch {
>>
>> /* Per-vcpu TLB for VNCR_EL2 -- NULL when !NV */
>> struct vncr_tlb *vncr_tlb;
>> +
>> + /* 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 6c13847480f7..4e2c61e71a38 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -63,6 +63,26 @@ 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
>> + */
>> +struct realm_rec {
>> + unsigned long mpidr;
>> + void *rec_page;
>> + /*
>> + * REC_PARAMS_AUX_GRANULES is the maximum number of 4K granules that
>> + * the RMM can require. The array is sized to be large enough for the
>> + * maximum number of host sized pages that could be required.
>> + */
>> + struct page *aux_pages[(REC_PARAMS_AUX_GRANULES * SZ_4K) >> PAGE_SHIFT];
>> + struct rec_run *run;
>> +};
>> +
>> void kvm_init_rmi(void);
>> u32 kvm_realm_ipa_limit(void);
>>
>> @@ -70,6 +90,7 @@ int kvm_init_realm_vm(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 c8e51ed009c0..8c50ebd9fba0 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -575,6 +575,8 @@ 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 */
>> @@ -1549,7 +1551,7 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
>> return -EINVAL;
>> }
>>
>> -static unsigned long system_supported_vcpu_features(void)
>> +static unsigned long system_supported_vcpu_features(struct kvm *kvm)
>> {
>> unsigned long features = KVM_VCPU_VALID_FEATURES;
>>
>> @@ -1587,7 +1589,7 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>> return -ENOENT;
>> }
>>
>> - if (features & ~system_supported_vcpu_features())
>> + if (features & ~system_supported_vcpu_features(vcpu->kvm))
>
> Hi,
>
> Are these two hunks superfluous?

Ah, yes that's left over from a previous version - thanks for spotting.

Thanks,
Steve

> Thanks,
> Wei-Lin Chang
>
>> return -EINVAL;
>>
>> /*
>> @@ -1609,6 +1611,10 @@ 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 959532422d3a..4bbf58892928 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 937fababf960..6daf14c4b413 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -207,6 +207,28 @@ static int get_start_level(struct realm *realm)
>> return 4 - stage2_pgtable_levels(realm->ia_bits);
>> }
>>
>> +static int delegate_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_delegate(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 delegate_page(phys_addr_t phys)
>> +{
>> + return delegate_range(phys, PAGE_SIZE);
>> +}
>> +
>> static int undelegate_range(phys_addr_t phys, unsigned long size)
>> {
>> unsigned long ret;
>> @@ -372,9 +394,177 @@ static int realm_ensure_created(struct kvm *kvm)
>> return -ENXIO;
>> }
>>
>> +static void free_rec_aux(struct page **aux_pages,
>> + unsigned int num_aux)
>> +{
>> + unsigned int i;
>> + unsigned int page_count = 0;
>> +
>> + for (i = 0; i < num_aux; i++) {
>> + struct page *aux_page = aux_pages[page_count++];
>> + phys_addr_t aux_page_phys = page_to_phys(aux_page);
>> +
>> + if (!WARN_ON(undelegate_page(aux_page_phys)))
>> + __free_page(aux_page);
>> + aux_page_phys += PAGE_SIZE;
>> + }
>> +}
>> +
>> +static int alloc_rec_aux(struct page **aux_pages,
>> + u64 *aux_phys_pages,
>> + unsigned int num_aux)
>> +{
>> + struct page *aux_page;
>> + unsigned int i;
>> + int ret;
>> +
>> + for (i = 0; i < num_aux; i++) {
>> + phys_addr_t aux_page_phys;
>> +
>> + aux_page = alloc_page(GFP_KERNEL);
>> + if (!aux_page) {
>> + ret = -ENOMEM;
>> + goto out_err;
>> + }
>> +
>> + aux_page_phys = page_to_phys(aux_page);
>> + if (delegate_page(aux_page_phys)) {
>> + ret = -ENXIO;
>> + goto err_undelegate;
>> + }
>> + aux_phys_pages[i] = aux_page_phys;
>> + aux_pages[i] = aux_page;
>> + }
>> +
>> + return 0;
>> +err_undelegate:
>> + while (i > 0) {
>> + i--;
>> + if (WARN_ON(undelegate_page(aux_phys_pages[i]))) {
>> + /* Leak the page if the undelegate fails */
>> + goto out_err;
>> + }
>> + }
>> + __free_page(aux_page);
>> +out_err:
>> + free_rec_aux(aux_pages, i);
>> + return ret;
>> +}
>> +
>> +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);
>> + if (!params || !rec->rec_page || !rec->run) {
>> + 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 (delegate_page(rec_page_phys)) {
>> + r = -ENXIO;
>> + goto out_free_pages;
>> + }
>> +
>> + r = alloc_rec_aux(rec->aux_pages, params->aux, realm->num_aux);
>> + if (r)
>> + goto out_undelegate_rmm_rec;
>> +
>> + params->num_rec_aux = realm->num_aux;
>> + params->mpidr = mpidr;
>> +
>> + if (rmi_rec_create(virt_to_phys(realm->rd),
>> + rec_page_phys,
>> + virt_to_phys(params))) {
>> + r = -ENXIO;
>> + goto out_free_rec_aux;
>> + }
>> +
>> + rec->mpidr = mpidr;
>> +
>> + free_page((unsigned long)params);
>> + return 0;
>> +
>> +out_free_rec_aux:
>> + free_rec_aux(rec->aux_pages, realm->num_aux);
>> +out_undelegate_rmm_rec:
>> + if (WARN_ON(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);
>> + rec->run = NULL;
>> + return r;
>> +}
>> +
>> +void kvm_destroy_rec(struct kvm_vcpu *vcpu)
>> +{
>> + struct realm *realm = &vcpu->kvm->arch.realm;
>> + struct realm_rec *rec = &vcpu->arch.rec;
>> + unsigned long rec_page_phys;
>> +
>> + if (!vcpu_is_rec(vcpu))
>> + return;
>> +
>> + if (!rec->run) {
>> + /* Nothing to do if the VCPU hasn't been finalized */
>> + return;
>> + }
>> +
>> + free_page((unsigned long)rec->run);
>> +
>> + rec_page_phys = virt_to_phys(rec->rec_page);
>> +
>> + /*
>> + * The REC and any AUX pages cannot be reclaimed until the REC is
>> + * destroyed. So if the REC destroy fails then the REC page and any AUX
>> + * pages will be leaked.
>> + */
>> + if (WARN_ON(rmi_rec_destroy(rec_page_phys)))
>> + return;
>> +
>> + free_rec_aux(rec->aux_pages, realm->num_aux);
>> +
>> + free_delegated_page(rec_page_phys);
>> +}
>> +
>> int kvm_activate_realm(struct kvm *kvm)
>> {
>> struct realm *realm = &kvm->arch.realm;
>> + struct kvm_vcpu *vcpu;
>> + unsigned long i;
>> int ret;
>>
>> if (kvm_realm_state(kvm) >= REALM_STATE_ACTIVE)
>> @@ -397,6 +587,12 @@ int kvm_activate_realm(struct kvm *kvm)
>> /* Mark state as dead in case we fail */
>> WRITE_ONCE(realm->state, REALM_STATE_DEAD);
>>
>> + kvm_for_each_vcpu(i, vcpu, kvm) {
>> + ret = kvm_create_rec(vcpu);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> ret = rmi_realm_activate(virt_to_phys(realm->rd));
>> if (ret)
>> return -ENXIO;
>> --
>> 2.43.0
>>