Re: [PATCH v14 19/44] arm64: RMI: Allocate/free RECs to match vCPUs

[Steven Price]

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@xxxxxxx>
>> ---
>> 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