Re: [PATCH v7 20/45] arm64: RME: Allow populating initial contents

[Gavin Shan <gshan@redhat.com>]

On 2/14/25 2:14 AM, 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.
> 
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> 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/kvm/rme.c | 234 +++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 234 insertions(+)
> 

With the following comments addressed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index f965869e9ef7..7880894db722 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -624,6 +624,228 @@ void kvm_realm_unmap_range(struct kvm *kvm, unsigned long start, u64 size,
>   		realm_unmap_private_range(kvm, start, end);
>   }
>   
> +static int realm_create_protected_data_granule(struct realm *realm,
> +					       unsigned long ipa,
> +					       phys_addr_t dst_phys,
> +					       phys_addr_t src_phys,
> +					       unsigned long flags)
> +{
> +	phys_addr_t rd = virt_to_phys(realm->rd);
> +	int ret;
> +
> +	if (rmi_granule_delegate(dst_phys))
> +		return -ENXIO;
> +
> +	ret = rmi_data_create(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);
> +
> +		WARN_ON(level == RMM_RTT_MAX_LEVEL);
> +
> +		ret = realm_create_rtt_levels(realm, ipa, level,
> +					      RMM_RTT_MAX_LEVEL, NULL);
> +		if (ret)
> +			return -EIO;
> +
> +		ret = rmi_data_create(rd, dst_phys, ipa, src_phys, flags);
> +	}
> +	if (ret)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int realm_create_protected_data_page(struct realm *realm,
> +					    unsigned long ipa,
> +					    kvm_pfn_t dst_pfn,
> +					    kvm_pfn_t src_pfn,
> +					    unsigned long flags)
> +{
> +	unsigned long rd = virt_to_phys(realm->rd);
> +	phys_addr_t dst_phys, src_phys;
> +	bool undelegate_failed = false;
> +	int ret, offset;
> +
> +	dst_phys = __pfn_to_phys(dst_pfn);
> +	src_phys = __pfn_to_phys(src_pfn);
> +
> +	for (offset = 0; offset < PAGE_SIZE; offset += RMM_PAGE_SIZE) {
> +		ret = realm_create_protected_data_granule(realm,
> +							  ipa,
> +							  dst_phys,
> +							  src_phys,
> +							  flags);
> +		if (ret)
> +			goto err;
> +
> +		ipa += RMM_PAGE_SIZE;
> +		dst_phys += RMM_PAGE_SIZE;
> +		src_phys += RMM_PAGE_SIZE;
> +	}
> +
> +	return 0;
> +
> +err:
> +	if (ret == -EIO) {
> +		/* current offset needs undelegating */
> +		if (WARN_ON(rmi_granule_undelegate(dst_phys)))
> +			undelegate_failed = true;
> +	}
> +	while (offset > 0) {
> +		ipa -= RMM_PAGE_SIZE;
> +		offset -= RMM_PAGE_SIZE;
> +		dst_phys -= RMM_PAGE_SIZE;
> +
> +		rmi_data_destroy(rd, ipa, NULL, NULL);
> +
> +		if (WARN_ON(rmi_granule_undelegate(dst_phys)))
> +			undelegate_failed = true;
> +	}
> +
> +	if (undelegate_failed) {
> +		/*
> +		 * A granule could not be undelegated,
> +		 * so the page has to be leaked
> +		 */
> +		get_page(pfn_to_page(dst_pfn));
> +	}
> +
> +	return -ENXIO;
> +}
> +
> +static int populate_region(struct kvm *kvm,
> +			   phys_addr_t ipa_base,
> +			   phys_addr_t ipa_end,
> +			   unsigned long data_flags)
> +{
> +	struct realm *realm = &kvm->arch.realm;
> +	struct kvm_memory_slot *memslot;
> +	gfn_t base_gfn, end_gfn;
> +	int idx;
> +	phys_addr_t ipa;
> +	int ret = 0;
> +
> +	base_gfn = gpa_to_gfn(ipa_base);
> +	end_gfn = gpa_to_gfn(ipa_end);
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +	memslot = gfn_to_memslot(kvm, base_gfn);
> +	if (!memslot) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	/* We require the region to be contained within a single memslot */
> +	if (memslot->base_gfn + memslot->npages < end_gfn) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (!kvm_slot_can_be_private(memslot)) {
> +		ret = -EINVAL;
		ret = -EPERM;

> +		goto out;
> +	}
> +
> +	write_lock(&kvm->mmu_lock);
> +
> +	ipa = ALIGN_DOWN(ipa_base, PAGE_SIZE);

The aignment operation is unnecessary since the base/size are ensured
to be aligned to PAGE_SIZE by its caller (kvm_populate_realm()).

> +	while (ipa < ipa_end) {
> +		struct vm_area_struct *vma;
> +		unsigned long hva;
> +		struct page *page;
> +		bool writeable;
> +		kvm_pfn_t pfn;
> +		kvm_pfn_t priv_pfn;
> +		struct page *gmem_page;
> +
> +		hva = gfn_to_hva_memslot(memslot, gpa_to_gfn(ipa));
> +		vma = vma_lookup(current->mm, hva);
> +		if (!vma) {
> +			ret = -EFAULT;
> +			break;
> +		}
> +
> +		pfn = __kvm_faultin_pfn(memslot, gpa_to_gfn(ipa), FOLL_WRITE,
> +					&writeable, &page);
> +
> +		if (is_error_pfn(pfn)) {
> +			ret = -EFAULT;
> +			break;
> +		}
> +
> +		ret = kvm_gmem_get_pfn(kvm, memslot,
> +				       ipa >> PAGE_SHIFT,
> +				       &priv_pfn, &gmem_page, NULL);
> +		if (ret)
> +			break;
> +
> +		ret = realm_create_protected_data_page(realm, ipa,
> +						       priv_pfn,
> +						       pfn,
> +						       data_flags);
> +
> +		kvm_release_faultin_page(kvm, page, false, false);
> +
> +		if (ret)
> +			break;
> +
> +		ipa += PAGE_SIZE;
> +	}
> +
> +	write_unlock(&kvm->mmu_lock);
> +
> +out:
> +	srcu_read_unlock(&kvm->srcu, idx);
> +	return ret;
> +}
> +
> +static int kvm_populate_realm(struct kvm *kvm,
> +			      struct arm_rme_populate_realm *args)
> +{
> +	phys_addr_t ipa_base, ipa_end;
> +	unsigned long data_flags = 0;
> +
> +	if (kvm_realm_state(kvm) != REALM_STATE_NEW)
> +		return -EINVAL;
		return -EPERM;

> +
> +	if (!IS_ALIGNED(args->base, PAGE_SIZE) ||
> +	    !IS_ALIGNED(args->size, PAGE_SIZE))
> +		return -EINVAL;
> +
> +	if (args->flags & ~RMI_MEASURE_CONTENT)
> +		return -EINVAL;

It's perfect to combine those checks:

	if (!IS_ALIGNED(...) ||
	    !IS_ALIGNED(...) ||
	    args->flags & ~RMI_MEASURE_CONTENT)
		return -EINVAL;

> +
> +	ipa_base = args->base;
> +	ipa_end = ipa_base + args->size;
> +
> +	if (ipa_end < ipa_base)
> +		return -EINVAL;
> +
> +	if (args->flags & RMI_MEASURE_CONTENT)
> +		data_flags |= RMI_MEASURE_CONTENT;
> +
> +	/*
> +	 * Perform the populate in parts to ensure locks are not held for too
> +	 * long
> +	 */
	
s/populate/population ?

> +	while (ipa_base < ipa_end) {
> +		phys_addr_t end = min(ipa_end, ipa_base + SZ_2M);
> +
> +		int ret = populate_region(kvm, ipa_base, end,
> +					  args->flags);
> +
> +		if (ret)
> +			return ret;
> +
> +		ipa_base = end;
> +
> +		cond_resched();
> +	}
> +
> +	return 0;
> +}
> +
>   static int realm_set_ipa_state(struct kvm_vcpu *vcpu,
>   			       unsigned long start,
>   			       unsigned long end,
> @@ -873,6 +1095,18 @@ int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>   		r = kvm_init_ipa_range_realm(kvm, &args);
>   		break;
>   	}
> +	case KVM_CAP_ARM_RME_POPULATE_REALM: {
> +		struct arm_rme_populate_realm args;
> +		void __user *argp = u64_to_user_ptr(cap->args[1]);
> +
> +		if (copy_from_user(&args, argp, sizeof(args))) {
> +			r = -EFAULT;
> +			break;
> +		}
> +
> +		r = kvm_populate_realm(kvm, &args);
> +		break;
> +	}
>   	default:
>   		r = -EINVAL;
>   		break;

Thanks,
Gavin