Re: [PATCH v13 24/48] arm64: RMI: Allow populating initial contents

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 18/03/2026 15:53, Steven Price wrote:
> The VMM needs to populate the realm with some data before starting (e.g.
> a kernel and initrd). This is measured by the RMM and used as part of
> the attestation later on.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v12:
>   * The ioctl now updates the structure with the amount populated rather
>     than returning this through the ioctl return code.
>   * Use the new RMM v2.0 range based RMI calls.
>   * Adapt to upstream changes in kvm_gmem_populate().
> Changes since v11:
>   * The multiplex CAP is gone and there's a new ioctl which makes use of
>     the generic kvm_gmem_populate() functionality.
> Changes since v7:
>   * Improve the error codes.
>   * Other minor changes from review.
> Changes since v6:
>   * Handle host potentially having a larger page size than the RMM
>     granule.
>   * Drop historic "par" (protected address range) from
>     populate_par_region() - it doesn't exist within the current
>     architecture.
>   * Add a cond_resched() call in kvm_populate_realm().
> Changes since v5:
>   * Refactor to use PFNs rather than tracking struct page in
>     realm_create_protected_data_page().
>   * Pull changes from a later patch (in the v5 series) for accessing
>     pages from a guest memfd.
>   * Do the populate in chunks to avoid holding locks for too long and
>     triggering RCU stall warnings.
> ---
>   arch/arm64/include/asm/kvm_rmi.h |   4 ++
>   arch/arm64/kvm/Kconfig           |   1 +
>   arch/arm64/kvm/arm.c             |  13 ++++
>   arch/arm64/kvm/rmi.c             | 111 +++++++++++++++++++++++++++++++
>   4 files changed, 129 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
> index 46b0cbe6c202..bf663bb240c4 100644
> --- a/arch/arm64/include/asm/kvm_rmi.h
> +++ b/arch/arm64/include/asm/kvm_rmi.h
> @@ -96,6 +96,10 @@ int kvm_rec_enter(struct kvm_vcpu *vcpu);
>   int kvm_rec_pre_enter(struct kvm_vcpu *vcpu);
>   int handle_rec_exit(struct kvm_vcpu *vcpu, int rec_run_status);
>   
> +struct kvm_arm_rmi_populate;
> +
> +int kvm_arm_rmi_populate(struct kvm *kvm,
> +			 struct kvm_arm_rmi_populate *arg);
>   void kvm_realm_unmap_range(struct kvm *kvm,
>   			   unsigned long ipa,
>   			   unsigned long size,
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 1cac6dfc0972..b495dfd3a8b4 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -39,6 +39,7 @@ menuconfig KVM
>   	select GUEST_PERF_EVENTS if PERF_EVENTS
>   	select KVM_GUEST_MEMFD
>   	select KVM_GENERIC_MEMORY_ATTRIBUTES
> +	select HAVE_KVM_ARCH_GMEM_POPULATE
>   	help
>   	  Support hosting virtualized guest machines.
>   
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index badb94b398bc..43d05da7e694 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2089,6 +2089,19 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>   			return -EFAULT;
>   		return kvm_vm_ioctl_get_reg_writable_masks(kvm, &range);
>   	}
> +	case KVM_ARM_RMI_POPULATE: {
> +		struct kvm_arm_rmi_populate req;
> +		int ret;
> +
> +		if (!kvm_is_realm(kvm))
> +			return -ENXIO;
> +		if (copy_from_user(&req, argp, sizeof(req)))
> +			return -EFAULT;
> +		ret = kvm_arm_rmi_populate(kvm, &req);
> +		if (copy_to_user(argp, &req, sizeof(req)))
> +			return -EFAULT;
> +		return ret;
> +	}
>   	default:
>   		return -EINVAL;
>   	}
> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
> index 13eed6f0b9eb..b48f4e12e4e0 100644
> --- a/arch/arm64/kvm/rmi.c
> +++ b/arch/arm64/kvm/rmi.c
> @@ -718,6 +718,80 @@ void kvm_realm_unmap_range(struct kvm *kvm, unsigned long start,
>   		realm_unmap_private_range(kvm, start, end, may_block);
>   }
>   
> +static int realm_create_protected_data_page(struct kvm *kvm,

minor nit: To align with the RMM ABI, could we rename this to :

	realm_data_map_init() ?

> +					    unsigned long ipa,
> +					    kvm_pfn_t dst_pfn,
> +					    kvm_pfn_t src_pfn,
> +					    unsigned long flags)
> +{
> +	struct realm *realm = &kvm->arch.realm;
> +	phys_addr_t rd = virt_to_phys(realm->rd);
> +	phys_addr_t dst_phys, src_phys;
> +	int ret;
> +
> +	dst_phys = __pfn_to_phys(dst_pfn);
> +	src_phys = __pfn_to_phys(src_pfn);
> +
> +	if (delegate_page(dst_phys))
> +		return -ENXIO;
> +
> +	ret = rmi_rtt_data_map_init(rd, dst_phys, ipa, src_phys, flags);
> +	if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
> +		/* Create missing RTTs and retry */
> +		int level = RMI_RETURN_INDEX(ret);
> +
> +		KVM_BUG_ON(level == RMM_RTT_MAX_LEVEL, kvm);

A buggy VMM can trigger this by calling RMI_POPULATE twice ? Should we
return -ENXIO here rather ? The delegate_page() above could prevent
normal cases, but is the VMM allowed to somehow trigger a "pfn" change
backing the KVM ? Either way, this need not be Fatal ?

Otherwise looks good to me.

Suzuki


> +
> +		ret = realm_create_rtt_levels(realm, ipa, level,
> +					      RMM_RTT_MAX_LEVEL, NULL);
> +		if (!ret) {
> +			ret = rmi_rtt_data_map_init(rd, dst_phys, ipa, src_phys,
> +						    flags);
> +		}
> +	}
> +
> +	if (ret) {
> +		if (WARN_ON(undelegate_page(dst_phys))) {
> +			/* Undelegate failed, so we leak the page */
> +			get_page(pfn_to_page(dst_pfn));
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +static int populate_region_cb(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> +			      struct page *src_page, void *opaque)
> +{
> +	unsigned long data_flags = *(unsigned long *)opaque;
> +	phys_addr_t ipa = gfn_to_gpa(gfn);
> +
> +	if (!src_page)
> +		return -EOPNOTSUPP;
> +
> +	return realm_create_protected_data_page(kvm, ipa, pfn,
> +						page_to_pfn(src_page),
> +						data_flags);
> +}
> +
> +static long populate_region(struct kvm *kvm,
> +			    gfn_t base_gfn,
> +			    unsigned long pages,
> +			    u64 uaddr,
> +			    unsigned long data_flags)
> +{
> +	long ret = 0;
> +
> +	mutex_lock(&kvm->slots_lock);
> +	mmap_read_lock(current->mm);
> +	ret = kvm_gmem_populate(kvm, base_gfn, u64_to_user_ptr(uaddr), pages,
> +				populate_region_cb, &data_flags);
> +	mmap_read_unlock(current->mm);
> +	mutex_unlock(&kvm->slots_lock);
> +
> +	return ret;
> +}
> +
>   enum ripas_action {
>   	RIPAS_INIT,
>   	RIPAS_SET,
> @@ -815,6 +889,43 @@ static int realm_ensure_created(struct kvm *kvm)
>   	return -ENXIO;
>   }
>   
> +int kvm_arm_rmi_populate(struct kvm *kvm,
> +			 struct kvm_arm_rmi_populate *args)
> +{
> +	unsigned long data_flags = 0;
> +	unsigned long ipa_start = args->base;
> +	unsigned long ipa_end = ipa_start + args->size;
> +	long pages_populated;
> +	int ret;
> +
> +	if (args->reserved ||
> +	    (args->flags & ~KVM_ARM_RMI_POPULATE_FLAGS_MEASURE) ||
> +	    !IS_ALIGNED(ipa_start, PAGE_SIZE) ||
> +	    !IS_ALIGNED(ipa_end, PAGE_SIZE) ||
> +	    !IS_ALIGNED(args->source_uaddr, PAGE_SIZE))
> +		return -EINVAL;
> +
> +	ret = realm_ensure_created(kvm);
> +	if (ret)
> +		return ret;
> +
> +	if (args->flags & KVM_ARM_RMI_POPULATE_FLAGS_MEASURE)
> +		data_flags |= RMI_MEASURE_CONTENT;
> +
> +	pages_populated = populate_region(kvm, gpa_to_gfn(ipa_start),
> +					  args->size >> PAGE_SHIFT,
> +					  args->source_uaddr, data_flags);
> +
> +	if (pages_populated < 0)
> +		return pages_populated;
> +
> +	args->size -= pages_populated << PAGE_SHIFT;
> +	args->source_uaddr += pages_populated << PAGE_SHIFT;
> +	args->base += pages_populated << PAGE_SHIFT;
> +
> +	return 0;
> +}
> +
>   static void kvm_complete_ripas_change(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm *kvm = vcpu->kvm;