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

[Steven Price]

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@xxxxxxx>
>> ---
>> 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
>>