[PATCH v10 07/43] arm64: RME: ioctls to create and configure realms

Steven Price
2025-08-20T14:57:44Z

Add the KVM_CAP_ARM_RME_CREATE_RD ioctl to create a realm. This involves
delegating pages to the RMM to hold the Realm Descriptor (RD) and for
the base level of the Realm Translation Tables (RTT). A VMID also need
to be picked, since the RMM has a separate VMID address space a
dedicated allocator is added for this purpose.

KVM_CAP_ARM_RME_CONFIG_REALM is provided to allow configuring the realm
before it is created. Configuration options can be classified as:

1. Parameters specific to the Realm stage2 (e.g. IPA Size, vmid, stage2
entry level, entry level RTTs, number of RTTs in start level, LPA2)
Most of these are not measured by RMM and comes from KVM book
keeping.

2. Parameters controlling "Arm Architecture features for the VM". (e.g.
SVE VL, PMU counters, number of HW BRPs/WPs), configured by the VMM
using the "user ID register write" mechanism. These will be
supported in the later patches.

3. Parameters are not part of the core Arm architecture but defined
by the RMM spec (e.g. Hash algorithm for measurement,
Personalisation value). These are programmed via
KVM_CAP_ARM_RME_CONFIG_REALM.

For the IPA size there is the possibility that the RMM supports a
different size to the IPA size supported by KVM for normal guests. At
the moment the 'normal limit' is exposed by KVM_CAP_ARM_VM_IPA_SIZE and
the IPA size is configured by the bottom bits of vm_type in
KVM_CREATE_VM. This means that it isn't easy for the VMM to discover
what IPA sizes are supported for Realm guests. Since the IPA is part of
the measurement of the realm guest the current expectation is that the
VMM will be required to pick the IPA size demanded by attestation and
therefore simply failing if this isn't available is fine. An option
would be to expose a new capability ioctl to obtain the RMM's maximum
IPA size if this is needed in the future.

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>
Reviewed-by: Gavin Shan <gshan@redhat.com>
---
Changes since v9:
* Avoid walking the stage 2 page tables when destroying the realm -
the real ones are not accessible to the non-secure world, and the RMM
may leave junk in the physical pages when returning them.
* Fix an error path in realm_create_rd() to actually return an error value.
Changes since v8:
* Fix free_delegated_granule() to not call kvm_account_pgtable_pages();
a separate wrapper will be introduced in a later patch to deal with
RTTs.
* Minor code cleanups following review.
Changes since v7:
* Minor code cleanup following Gavin's review.
Changes since v6:
* Separate RMM RTT calculations from host PAGE_SIZE. This allows the
host page size to be larger than 4k while still communicating with an
RMM which uses 4k granules.
Changes since v5:
* Introduce free_delegated_granule() to replace many
undelegate/free_page() instances and centralise the comment on
leaking when the undelegate fails.
* Several other minor improvements suggested by reviews - thanks for
the feedback!
Changes since v2:
* Improved commit description.
* Improved return failures for rmi_check_version().
* Clear contents of PGD after it has been undelegated in case the RMM
left stale data.
* Minor changes to reflect changes in previous patches.
---
arch/arm64/include/asm/kvm_emulate.h | 5 +
arch/arm64/include/asm/kvm_rme.h | 19 ++
arch/arm64/kvm/arm.c | 16 ++
arch/arm64/kvm/mmu.c | 24 +-
arch/arm64/kvm/rme.c | 322 +++++++++++++++++++++++++++
5 files changed, 383 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index ab4093e41c4b..f429ad704850 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -687,6 +687,11 @@ static inline enum realm_state kvm_realm_state(struct kvm *kvm)
return READ_ONCE(kvm->arch.realm.state);
}

+static inline bool kvm_realm_is_created(struct kvm *kvm)
+{
+ return kvm_is_realm(kvm) && kvm_realm_state(kvm) != REALM_STATE_NONE;
+}
+
static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
{
return false;
diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
index 9c8a0b23e0e4..5dc1915de891 100644
--- a/arch/arm64/include/asm/kvm_rme.h
+++ b/arch/arm64/include/asm/kvm_rme.h
@@ -6,6 +6,8 @@
#ifndef __ASM_KVM_RME_H
#define __ASM_KVM_RME_H

+#include <uapi/linux/kvm.h>
+
/**
* enum realm_state - State of a Realm
*/
@@ -46,11 +48,28 @@ enum realm_state {
* struct realm - Additional per VM data for a Realm
*
* @state: The lifetime state machine for the realm
+ * @rd: Kernel mapping of the Realm Descriptor (RD)
+ * @params: Parameters for the RMI_REALM_CREATE command
+ * @num_aux: The number of auxiliary pages required by the RMM
+ * @vmid: VMID to be used by the RMM for the realm
+ * @ia_bits: Number of valid Input Address bits in the IPA
*/
struct realm {
enum realm_state state;
+
+ void *rd;
+ struct realm_params *params;
+
+ unsigned long num_aux;
+ unsigned int vmid;
+ unsigned int ia_bits;
};

void kvm_init_rme(void);
+u32 kvm_realm_ipa_limit(void);
+
+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);

#endif /* __ASM_KVM_RME_H */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 76177c56f1ef..1acee3861e55 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -136,6 +136,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
}
mutex_unlock(&kvm->lock);
break;
+ case KVM_CAP_ARM_RME:
+ mutex_lock(&kvm->lock);
+ r = kvm_realm_enable_cap(kvm, cap);
+ mutex_unlock(&kvm->lock);
+ break;
default:
break;
}
@@ -198,6 +203,13 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)

bitmap_zero(kvm->arch.vcpu_features, KVM_VCPU_MAX_FEATURES);

+ /* Initialise the realm bits after the generic bits are enabled */
+ if (kvm_is_realm(kvm)) {
+ ret = kvm_init_realm_vm(kvm);
+ if (ret)
+ goto err_free_cpumask;
+ }
+
return 0;

err_free_cpumask:
@@ -257,6 +269,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kvm_unshare_hyp(kvm, kvm + 1);

kvm_arm_teardown_hypercalls(kvm);
+ kvm_destroy_realm(kvm);
}

static bool kvm_has_full_ptr_auth(void)
@@ -417,6 +430,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
else
r = kvm_supports_cacheable_pfnmap();
break;
+ case KVM_CAP_ARM_RME:
+ r = static_key_enabled(&kvm_rme_is_available);
+ break;

default:
r = 0;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1c78864767c5..de10dbde4761 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -871,12 +871,16 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
.icache_inval_pou = invalidate_icache_guest_page,
};

-static int kvm_init_ipa_range(struct kvm_s2_mmu *mmu, unsigned long type)
+static int kvm_init_ipa_range(struct kvm *kvm,
+ struct kvm_s2_mmu *mmu, unsigned long type)
{
u32 kvm_ipa_limit = get_kvm_ipa_limit();
u64 mmfr0, mmfr1;
u32 phys_shift;

+ if (kvm_is_realm(kvm))
+ kvm_ipa_limit = kvm_realm_ipa_limit();
+
if (type & ~KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
return -EINVAL;

@@ -941,7 +945,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
return -EINVAL;
}

- err = kvm_init_ipa_range(mmu, type);
+ err = kvm_init_ipa_range(kvm, mmu, type);
if (err)
return err;

@@ -1067,6 +1071,19 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
struct kvm_pgtable *pgt = NULL;

write_lock(&kvm->mmu_lock);
+ if (kvm_is_realm(kvm) &&
+ (kvm_realm_state(kvm) != REALM_STATE_DEAD &&
+ kvm_realm_state(kvm) != REALM_STATE_NONE)) {
+ /* Tearing down RTTs will be added in a later patch */
+ write_unlock(&kvm->mmu_lock);
+
+ /*
+ * The PGD pages can be reclaimed only after the realm (RD) is
+ * destroyed. We call this again from kvm_destroy_realm() after
+ * the RD is destroyed.
+ */
+ return;
+ }
pgt = mmu->pgt;
if (pgt) {
mmu->pgd_phys = 0;
@@ -1076,7 +1093,8 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
write_unlock(&kvm->mmu_lock);

if (pgt) {
- KVM_PGT_FN(kvm_pgtable_stage2_destroy)(pgt);
+ if (!kvm_is_realm(kvm))
+ KVM_PGT_FN(kvm_pgtable_stage2_destroy)(pgt);
kfree(pgt);
}
}
diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
index 67cf2d94cb2d..4a2c557bf0a7 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -5,9 +5,23 @@

#include <linux/kvm_host.h>

+#include <asm/kvm_emulate.h>
+#include <asm/kvm_mmu.h>
#include <asm/rmi_cmds.h>
#include <asm/virt.h>

+#include <asm/kvm_pgtable.h>
+
+static unsigned long rmm_feat_reg0;
+
+#define RMM_PAGE_SHIFT 12
+#define RMM_PAGE_SIZE BIT(RMM_PAGE_SHIFT)
+
+static bool rme_has_feature(unsigned long feature)
+{
+ return !!u64_get_bits(rmm_feat_reg0, feature);
+}
+
static int rmi_check_version(void)
{
struct arm_smccc_res res;
@@ -42,6 +56,308 @@ static int rmi_check_version(void)
return 0;
}

+u32 kvm_realm_ipa_limit(void)
+{
+ return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
+}
+
+static int get_start_level(struct realm *realm)
+{
+ /*
+ * Open coded version of 4 - stage2_pgtable_levels(ia_bits) but using
+ * the RMM's page size rather than the host's.
+ */
+ return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
+}
+
+static int free_delegated_granule(phys_addr_t phys)
+{
+ if (WARN_ON(rmi_granule_undelegate(phys))) {
+ /* Undelegate failed: leak the page */
+ return -EBUSY;
+ }
+
+ free_page((unsigned long)phys_to_virt(phys));
+
+ return 0;
+}
+
+/* Calculate the number of s2 root rtts needed */
+static int realm_num_root_rtts(struct realm *realm)
+{
+ unsigned int ipa_bits = realm->ia_bits;
+ unsigned int levels = 4 - get_start_level(realm);
+ unsigned int sl_ipa_bits = levels * (RMM_PAGE_SHIFT - 3) +
+ RMM_PAGE_SHIFT;
+
+ if (sl_ipa_bits >= ipa_bits)
+ return 1;
+
+ return 1 << (ipa_bits - sl_ipa_bits);
+}
+
+static int realm_create_rd(struct kvm *kvm)
+{
+ struct realm *realm = &kvm->arch.realm;
+ struct realm_params *params = realm->params;
+ void *rd = NULL;
+ phys_addr_t rd_phys, params_phys;
+ size_t pgd_size = kvm_pgtable_stage2_pgd_size(kvm->arch.mmu.vtcr);
+ int i, r;
+ int rtt_num_start;
+
+ realm->ia_bits = VTCR_EL2_IPA(kvm->arch.mmu.vtcr);
+ rtt_num_start = realm_num_root_rtts(realm);
+
+ if (WARN_ON(realm->rd || !realm->params))
+ return -EEXIST;
+
+ if (pgd_size / RMM_PAGE_SIZE < rtt_num_start)
+ return -EINVAL;
+
+ rd = (void *)__get_free_page(GFP_KERNEL);
+ if (!rd)
+ return -ENOMEM;
+
+ rd_phys = virt_to_phys(rd);
+ if (rmi_granule_delegate(rd_phys)) {
+ r = -ENXIO;
+ goto free_rd;
+ }
+
+ for (i = 0; i < pgd_size; i += RMM_PAGE_SIZE) {
+ phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i;
+
+ if (rmi_granule_delegate(pgd_phys)) {
+ r = -ENXIO;
+ goto out_undelegate_tables;
+ }
+ }
+
+ params->s2sz = VTCR_EL2_IPA(kvm->arch.mmu.vtcr);
+ params->rtt_level_start = get_start_level(realm);
+ params->rtt_num_start = rtt_num_start;
+ params->rtt_base = kvm->arch.mmu.pgd_phys;
+ params->vmid = realm->vmid;
+
+ params_phys = virt_to_phys(params);
+
+ if (rmi_realm_create(rd_phys, params_phys)) {
+ r = -ENXIO;
+ goto out_undelegate_tables;
+ }
+
+ if (WARN_ON(rmi_rec_aux_count(rd_phys, &realm->num_aux))) {
+ WARN_ON(rmi_realm_destroy(rd_phys));
+ r = -ENXIO;
+ goto out_undelegate_tables;
+ }
+
+ realm->rd = rd;
+
+ return 0;
+
+out_undelegate_tables:
+ while (i > 0) {
+ i -= RMM_PAGE_SIZE;
+
+ phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i;
+
+ if (WARN_ON(rmi_granule_undelegate(pgd_phys))) {
+ /* Leak the pages if they cannot be returned */
+ kvm->arch.mmu.pgt = NULL;
+ break;
+ }
+ }
+ if (WARN_ON(rmi_granule_undelegate(rd_phys))) {
+ /* Leak the page if it isn't returned */
+ return r;
+ }
+free_rd:
+ free_page((unsigned long)rd);
+ return r;
+}
+
+/* Protects access to rme_vmid_bitmap */
+static DEFINE_SPINLOCK(rme_vmid_lock);
+static unsigned long *rme_vmid_bitmap;
+
+static int rme_vmid_init(void)
+{
+ unsigned int vmid_count = 1 << kvm_get_vmid_bits();
+
+ rme_vmid_bitmap = bitmap_zalloc(vmid_count, GFP_KERNEL);
+ if (!rme_vmid_bitmap) {
+ kvm_err("%s: Couldn't allocate rme vmid bitmap\n", __func__);
+ return -ENOMEM;
+ }
+
+ return 0;
+}
+
+static int rme_vmid_reserve(void)
+{
+ int ret;
+ unsigned int vmid_count = 1 << kvm_get_vmid_bits();
+
+ spin_lock(&rme_vmid_lock);
+ ret = bitmap_find_free_region(rme_vmid_bitmap, vmid_count, 0);
+ spin_unlock(&rme_vmid_lock);
+
+ return ret;
+}
+
+static void rme_vmid_release(unsigned int vmid)
+{
+ spin_lock(&rme_vmid_lock);
+ bitmap_release_region(rme_vmid_bitmap, vmid, 0);
+ spin_unlock(&rme_vmid_lock);
+}
+
+static int kvm_create_realm(struct kvm *kvm)
+{
+ struct realm *realm = &kvm->arch.realm;
+ int ret;
+
+ if (kvm_realm_is_created(kvm))
+ return -EEXIST;
+
+ ret = rme_vmid_reserve();
+ if (ret < 0)
+ return ret;
+ realm->vmid = ret;
+
+ ret = realm_create_rd(kvm);
+ if (ret) {
+ rme_vmid_release(realm->vmid);
+ return ret;
+ }
+
+ WRITE_ONCE(realm->state, REALM_STATE_NEW);
+
+ /* The realm is up, free the parameters. */
+ free_page((unsigned long)realm->params);
+ realm->params = NULL;
+
+ return 0;
+}
+
+static int config_realm_hash_algo(struct realm *realm,
+ struct arm_rme_config *cfg)
+{
+ switch (cfg->hash_algo) {
+ case ARM_RME_CONFIG_HASH_ALGO_SHA256:
+ if (!rme_has_feature(RMI_FEATURE_REGISTER_0_HASH_SHA_256))
+ return -EINVAL;
+ break;
+ case ARM_RME_CONFIG_HASH_ALGO_SHA512:
+ if (!rme_has_feature(RMI_FEATURE_REGISTER_0_HASH_SHA_512))
+ return -EINVAL;
+ break;
+ default:
+ return -EINVAL;
+ }
+ realm->params->hash_algo = cfg->hash_algo;
+ return 0;
+}
+
+static int kvm_rme_config_realm(struct kvm *kvm, struct kvm_enable_cap *cap)
+{
+ struct arm_rme_config cfg;
+ struct realm *realm = &kvm->arch.realm;
+ int r = 0;
+
+ if (kvm_realm_is_created(kvm))
+ return -EBUSY;
+
+ if (copy_from_user(&cfg, (void __user *)cap->args[1], sizeof(cfg)))
+ return -EFAULT;
+
+ switch (cfg.cfg) {
+ case ARM_RME_CONFIG_RPV:
+ memcpy(&realm->params->rpv, &cfg.rpv, sizeof(cfg.rpv));
+ break;
+ case ARM_RME_CONFIG_HASH_ALGO:
+ r = config_realm_hash_algo(realm, &cfg);
+ break;
+ default:
+ r = -EINVAL;
+ }
+
+ return r;
+}
+
+int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
+{
+ int r = 0;
+
+ if (!kvm_is_realm(kvm))
+ return -EINVAL;
+
+ switch (cap->args[0]) {
+ case KVM_CAP_ARM_RME_CONFIG_REALM:
+ r = kvm_rme_config_realm(kvm, cap);
+ break;
+ case KVM_CAP_ARM_RME_CREATE_REALM:
+ r = kvm_create_realm(kvm);
+ break;
+ default:
+ r = -EINVAL;
+ break;
+ }
+
+ return r;
+}
+
+void kvm_destroy_realm(struct kvm *kvm)
+{
+ struct realm *realm = &kvm->arch.realm;
+ size_t pgd_size = kvm_pgtable_stage2_pgd_size(kvm->arch.mmu.vtcr);
+ int i;
+
+ if (realm->params) {
+ free_page((unsigned long)realm->params);
+ realm->params = NULL;
+ }
+
+ if (!kvm_realm_is_created(kvm))
+ return;
+
+ WRITE_ONCE(realm->state, REALM_STATE_DYING);
+
+ if (realm->rd) {
+ phys_addr_t rd_phys = virt_to_phys(realm->rd);
+
+ if (WARN_ON(rmi_realm_destroy(rd_phys)))
+ return;
+ free_delegated_granule(rd_phys);
+ realm->rd = NULL;
+ }
+
+ rme_vmid_release(realm->vmid);
+
+ for (i = 0; i < pgd_size; i += RMM_PAGE_SIZE) {
+ phys_addr_t pgd_phys = kvm->arch.mmu.pgd_phys + i;
+
+ if (WARN_ON(rmi_granule_undelegate(pgd_phys)))
+ return;
+ }
+
+ WRITE_ONCE(realm->state, REALM_STATE_DEAD);
+
+ /* Now that the Realm is destroyed, free the entry level RTTs */
+ kvm_free_stage2_pgd(&kvm->arch.mmu);
+}
+
+int kvm_init_realm_vm(struct kvm *kvm)
+{
+ kvm->arch.realm.params = (void *)get_zeroed_page(GFP_KERNEL);
+
+ if (!kvm->arch.realm.params)
+ return -ENOMEM;
+ return 0;
+}
+
void kvm_init_rme(void)
{
if (PAGE_SIZE != SZ_4K)
@@ -52,5 +368,11 @@ void kvm_init_rme(void)
/* Continue without realm support */
return;

+ if (WARN_ON(rmi_features(0, &rmm_feat_reg0)))
+ return;
+
+ if (rme_vmid_init())
+ return;
+
/* Future patch will enable static branch kvm_rme_is_available */
}
--
2.43.0