Re: [PATCH v9 11/43] arm64: RME: Allocate/free RECs to match vCPUs

[Joey Gouly <joey.gouly@arm.com>]

Hi Steven,

On Wed, Jun 11, 2025 at 11:48:08AM +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 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). The RMM also
> requires that the VMM creates RECs in ascending order of the MPIDR.
> 
> See Realm Management Monitor specification (DEN0137) for more information:
> https://developer.arm.com/documentation/den0137/
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> ---
> 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 |   7 ++
>  arch/arm64/include/asm/kvm_host.h    |   3 +
>  arch/arm64/include/asm/kvm_rme.h     |  27 ++++
>  arch/arm64/kvm/arm.c                 |  13 +-
>  arch/arm64/kvm/reset.c               |  11 ++
>  arch/arm64/kvm/rme.c                 | 180 +++++++++++++++++++++++++++
>  6 files changed, 239 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index a640bb7dffbc..302a691b3723 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -711,7 +711,14 @@ static inline bool kvm_realm_is_created(struct kvm *kvm)
>  
>  static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
>  {
> +	if (static_branch_unlikely(&kvm_rme_is_available))
> +		return vcpu_has_feature(vcpu, KVM_ARM_VCPU_REC);
>  	return false;
>  }
>  
> +static inline bool kvm_arm_rec_finalized(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.rec.mpidr != INVALID_HWID;
> +}
> +
>  #endif /* __ARM64_KVM_EMULATE_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 18e6d72dabe9..58fe7b216126 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -883,6 +883,9 @@ 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_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index 5f0de9a6d339..f716b890e484 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -6,6 +6,7 @@
>  #ifndef __ASM_KVM_RME_H
>  #define __ASM_KVM_RME_H
>  
> +#include <asm/rmi_smc.h>
>  #include <uapi/linux/kvm.h>
>  
>  /**
> @@ -65,6 +66,30 @@ 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 granules that the
> +	 * RMM can require. By using that to size the array we know that it
> +	 * will be big enough as the page size is always at least as large as
> +	 * the granule size. In the case of a larger page size than 4k (or an
> +	 * RMM which requires fewer auxiliary granules), the array will be
> +	 * bigger than needed however the extra memory required is small and
> +	 * this keeps the code cleaner.
> +	 */
> +	struct page *aux_pages[REC_PARAMS_AUX_GRANULES];

I think that something like this may work, and use the right amount of pages:

	struct page *aux_pages[(REC_PARAMS_AUX_GRANULES * RMM_PAGE_SIZE) >> PAGE_SHIFT];

Thanks,
Joey

> +	struct rec_run *run;
> +};
> +
>  void kvm_init_rme(void);
>  u32 kvm_realm_ipa_limit(void);
>  
> @@ -72,6 +97,8 @@ int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>  int kvm_init_realm_vm(struct kvm *kvm);
>  void kvm_destroy_realm(struct kvm *kvm);
>  void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits);
> +int kvm_create_rec(struct kvm_vcpu *vcpu);
> +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 b3e3323573c6..7be1bdfc5f0b 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -495,6 +495,8 @@ 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 */
> @@ -1457,7 +1459,7 @@ 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;
>  
> @@ -1478,6 +1480,9 @@ static unsigned long system_supported_vcpu_features(void)
>  	if (!cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
>  		clear_bit(KVM_ARM_VCPU_HAS_EL2, &features);
>  
> +	if (!kvm_is_realm(kvm))
> +		clear_bit(KVM_ARM_VCPU_REC, &features);
> +
>  	return features;
>  }
>  
> @@ -1495,7 +1500,7 @@ 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))
>  		return -EINVAL;
>  
>  	/*
> @@ -1517,6 +1522,10 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
>  	if (test_bit(KVM_ARM_VCPU_HAS_EL2, &features))
>  		return -EINVAL;
>  
> +	/* RME is incompatible with AArch32 */
> +	if (test_bit(KVM_ARM_VCPU_REC, &features))
> +		return -EINVAL;
> +
>  	return 0;
>  }
>  
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 959532422d3a..2e9e855581d4 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -137,6 +137,11 @@ int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int feature)
>  			return -EPERM;
>  
>  		return kvm_vcpu_finalize_sve(vcpu);
> +	case KVM_ARM_VCPU_REC:
> +		if (!kvm_is_realm(vcpu->kvm) || !vcpu_is_rec(vcpu))
> +			return -EINVAL;
> +
> +		return kvm_create_rec(vcpu);
>  	}
>  
>  	return -EINVAL;
> @@ -147,6 +152,11 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu)
>  	if (vcpu_has_sve(vcpu) && !kvm_arm_vcpu_sve_finalized(vcpu))
>  		return false;
>  
> +	if (kvm_is_realm(vcpu->kvm) &&
> +	    !(vcpu_is_rec(vcpu) && kvm_arm_rec_finalized(vcpu) &&
> +	      READ_ONCE(vcpu->kvm->arch.realm.state) == REALM_STATE_ACTIVE))
> +		return false;
> +
>  	return true;
>  }
>  
> @@ -161,6 +171,7 @@ 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/rme.c b/arch/arm64/kvm/rme.c
> index 0f89295fa59c..f094544592b5 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -484,6 +484,186 @@ void kvm_destroy_realm(struct kvm *kvm)
>  	kvm_free_stage2_pgd(&kvm->arch.mmu);
>  }
>  
> +static void free_rec_aux(struct page **aux_pages,
> +			 unsigned int num_aux)
> +{
> +	unsigned int i, j;
> +	unsigned int page_count = 0;
> +
> +	for (i = 0; i < num_aux;) {
> +		struct page *aux_page = aux_pages[page_count++];
> +		phys_addr_t aux_page_phys = page_to_phys(aux_page);
> +		bool should_free = true;
> +
> +		for (j = 0; j < PAGE_SIZE && i < num_aux; j += RMM_PAGE_SIZE) {
> +			if (WARN_ON(rmi_granule_undelegate(aux_page_phys)))
> +				should_free = false;
> +			aux_page_phys += RMM_PAGE_SIZE;
> +			i++;
> +		}
> +		/* Only free if all the undelegate calls were successful */
> +		if (should_free)
> +			__free_page(aux_page);
> +	}
> +}
> +
> +static int alloc_rec_aux(struct page **aux_pages,
> +			 u64 *aux_phys_pages,
> +			 unsigned int num_aux)
> +{
> +	struct page *aux_page;
> +	int page_count = 0;
> +	unsigned int i, j;
> +	int ret;
> +
> +	for (i = 0; i < num_aux;) {
> +		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);
> +		for (j = 0; j < PAGE_SIZE && i < num_aux; j += RMM_PAGE_SIZE) {
> +			if (rmi_granule_delegate(aux_page_phys)) {
> +				ret = -ENXIO;
> +				goto err_undelegate;
> +			}
> +			aux_phys_pages[i++] = aux_page_phys;
> +			aux_page_phys += RMM_PAGE_SIZE;
> +		}
> +		aux_pages[page_count++] = aux_page;
> +	}
> +
> +	return 0;
> +err_undelegate:
> +	while (j > 0) {
> +		j -= RMM_PAGE_SIZE;
> +		i--;
> +		if (WARN_ON(rmi_granule_undelegate(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;
> +}
> +
> +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 (kvm_realm_state(vcpu->kvm) != REALM_STATE_NEW)
> +		return -ENOENT;
> +
> +	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 (rmi_granule_delegate(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(rmi_granule_undelegate(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);
> +	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_granule(rec_page_phys);
> +}
> +
>  int kvm_init_realm_vm(struct kvm *kvm)
>  {
>  	kvm->arch.realm.params = (void *)get_zeroed_page(GFP_KERNEL);
> -- 
> 2.43.0
>