[PATCH v12 20/46] arm64: RMI: Allow populating initial contents
Steven Price
steven.price at arm.com
Mon Mar 2 08:46:52 PST 2026
On 02/03/2026 14:56, Marc Zyngier wrote:
> On Wed, 17 Dec 2025 10:10:57 +0000,
> Steven Price <steven.price at arm.com> 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 at arm.com>
>> ---
>> 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 | 9 ++
>> arch/arm64/kvm/rmi.c | 175 +++++++++++++++++++++++++++++++
>> 4 files changed, 189 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
>> index 8a862fc1a99d..b5e36344975c 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -99,6 +99,10 @@ 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 7927181887cf..0a06ed9d1a64 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -2037,6 +2037,15 @@ 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;
>> +
>> + if (!kvm_is_realm(kvm))
>> + return -EPERM;
>
> EPERM is odd. It isn't that the VMM doesn't have the right to do it,
> it is that it shouldn't have called that, because the ioctl doesn't
> exist for a normal VM. -ENOSYS?
Ack
>> + if (copy_from_user(&req, argp, sizeof(req)))
>> + return -EFAULT;
>> + return kvm_arm_rmi_populate(kvm, &req);
>> + }
>> default:
>> return -EINVAL;
>> }
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> index fe15b400091c..39577e956a59 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -558,6 +558,150 @@ 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_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);
>
> If this is unexpected, why do we still try to handle it? We should
> abort hard on anything that doesn't seem 100% correct, and mark the
> realm dead.
Well this is a "should never happen - the RMM (or Linux kerne) is buggy"
situation - so it's not specifically the realm's fault. The "do nothing"
error handling deals with things quite reasonably - the following
realm_create_rtt_levels() call is a no-op, so we'll retry the
rmi_data_create() call and bubble the error up.
I'll change this to KVM_BUG_ON so that the guest is killed just in case
it turns out the guest can somehow trigger this maliciously.
>> +
>> + 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_cb(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
>> + void __user *src, int order, void *opaque)
>> +{
>> + struct realm *realm = &kvm->arch.realm;
>> + unsigned long data_flags = *(unsigned long *)opaque;
>> + phys_addr_t ipa = gfn_to_gpa(gfn);
>> + int npages = (1 << order);
>> + int i;
>> +
>> + for (i = 0; i < npages; i++) {
>> + struct page *src_page;
>> + int ret;
>> +
>> + ret = get_user_pages((unsigned long)src, 1, 0, &src_page);
>> + if (ret < 0)
>> + return ret;
>> + if (ret != 1)
>> + return -ENOMEM;
>> +
>> + ret = realm_create_protected_data_page(realm, ipa, pfn,
>> + page_to_pfn(src_page),
>> + data_flags);
>> +
>> + put_page(src_page);
>> +
>> + if (ret)
>> + return ret;
>> +
>> + ipa += PAGE_SIZE;
>> + pfn++;
>> + src += PAGE_SIZE;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +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,
>> @@ -655,6 +799,37 @@ 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;
>> + 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))
>> + return -EINVAL;
>> +
>> + ret = realm_ensure_created(kvm);
>> + if (ret)
>> + return ret;
>> +
>> + if (args->flags & KVM_ARM_RMI_POPULATE_FLAGS_MEASURE)
>
> This flag isn't documented.
Indeed - that's an oversight! I'll add the following to the docs:
`flags` can be set to `KVM_ARM_RMI_POPULATE_FLAGS_MEASURE` to request that the
populated data is hashed and added to the guest's Realm Initial Measurement
(RIM).
>> + data_flags |= RMI_MEASURE_CONTENT;
>> +
>> + ret = populate_region(kvm, gpa_to_gfn(ipa_start),
>> + args->size >> PAGE_SHIFT,
>> + args->source_uaddr, args->flags);
>> +
>> + if (ret < 0)
>> + return ret;
>> +
>> + return ret * PAGE_SIZE;
>
> Bits of the code works on PAGE_SIZE, other bits on RMM_PAGE_SIZE. It
> is pretty confusing. Are you in the middle of reworking this?
Yes, sorry about that - RMM_PAGE_SIZE will be completely gone when
this is updated to RMM v2.0.
Thanks,
Steve
More information about the linux-arm-kernel
mailing list