[PATCH v13 12/48] arm64: RMI: Basic infrastructure for creating a realm.

Steven Price
2026-03-18T15:55:10Z

Introduce the skeleton functions for creating and destroying a realm.
The IPA size requested is checked against what the RMM supports.

The actual work of constructing the realm will be added in future
patches.

Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v12:
* Drop the RMM_PAGE_{SHIFT,SIZE} defines - the RMM is now configured to
be the same as the host's page size.
* Rework delegate/undelegate functions to use the new RMI range based
operations.
Changes since v11:
* Major rework to drop the realm configuration and make the
construction of realms implicit rather than driven by the VMM
directly.
* The code to create RDs, handle VMIDs etc is moved to later patches.
Changes since v10:
* Rename from RME to RMI.
* Move the stage2 cleanup to a later patch.
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_rmi.h | 16 +++++
arch/arm64/kvm/arm.c | 12 ++++
arch/arm64/kvm/mmu.c | 11 +++-
arch/arm64/kvm/rmi.c | 88 ++++++++++++++++++++++++++++
5 files changed, 129 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index f38b50151ce8..39310d9b4e16 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -701,6 +701,11 @@ 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_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
index 3506f50b05cd..0ada525af18f 100644
--- a/arch/arm64/include/asm/kvm_rmi.h
+++ b/arch/arm64/include/asm/kvm_rmi.h
@@ -6,6 +6,8 @@
#ifndef __ASM_KVM_RMI_H
#define __ASM_KVM_RMI_H

+#include <asm/rmi_smc.h>
+
/**
* enum realm_state - State of a Realm
*/
@@ -46,11 +48,25 @@ 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
+ * @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 ia_bits;
};

void kvm_init_rmi(void);
+u32 kvm_realm_ipa_limit(void);
+
+int kvm_init_realm_vm(struct kvm *kvm);
+void kvm_destroy_realm(struct kvm *kvm);

#endif /* __ASM_KVM_RMI_H */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 274d7866efdc..9b17bdfaf0c2 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -253,6 +253,13 @@ 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:
@@ -312,6 +319,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kvm_unshare_hyp(kvm, kvm + 1);

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

static bool kvm_has_full_ptr_auth(void)
@@ -473,6 +482,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
else
r = kvm_supports_cacheable_pfnmap();
break;
+ case KVM_CAP_ARM_RMI:
+ r = static_key_enabled(&kvm_rmi_is_available);
+ break;

default:
r = 0;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 070a01e53fcb..d6094b60c4ce 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -872,12 +872,16 @@ 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;

@@ -974,7 +978,7 @@ 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;

@@ -1113,7 +1117,8 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
write_unlock(&kvm->mmu_lock);

if (pgt) {
- kvm_stage2_destroy(pgt);
+ if (!kvm_is_realm(kvm))
+ kvm_stage2_destroy(pgt);
kfree(pgt);
}
}
diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
index 80aedc85e94a..700b8c935d29 100644
--- a/arch/arm64/kvm/rmi.c
+++ b/arch/arm64/kvm/rmi.c
@@ -6,6 +6,8 @@
#include <linux/kvm_host.h>
#include <linux/memblock.h>

+#include <asm/kvm_emulate.h>
+#include <asm/kvm_mmu.h>
#include <asm/kvm_pgtable.h>
#include <asm/rmi_cmds.h>
#include <asm/virt.h>
@@ -182,6 +184,92 @@ static int rmi_init_metadata(void)
return 0;
}

+u32 kvm_realm_ipa_limit(void)
+{
+ return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
+}
+
+static int undelegate_range(phys_addr_t phys, unsigned long size)
+{
+ unsigned long ret;
+ unsigned long top = phys + size;
+ unsigned long out_top;
+
+ while (phys < top) {
+ ret = rmi_granule_range_undelegate(phys, top, &out_top);
+ if (ret == RMI_SUCCESS)
+ phys = out_top;
+ else if (ret != RMI_BUSY && ret != RMI_BLOCKED)
+ return ret;
+ }
+
+ return ret;
+}
+
+static int undelegate_page(phys_addr_t phys)
+{
+ return undelegate_range(phys, PAGE_SIZE);
+}
+
+static int free_delegated_page(phys_addr_t phys)
+{
+ if (WARN_ON(undelegate_page(phys))) {
+ /* Undelegate failed: leak the page */
+ return -EBUSY;
+ }
+
+ free_page((unsigned long)phys_to_virt(phys));
+
+ return 0;
+}
+
+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);
+
+ write_lock(&kvm->mmu_lock);
+ kvm_stage2_unmap_range(&kvm->arch.mmu, 0,
+ BIT(realm->ia_bits - 1), true);
+ write_unlock(&kvm->mmu_lock);
+
+ 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_page(rd_phys);
+ realm->rd = NULL;
+ }
+
+ if (WARN_ON(undelegate_range(kvm->arch.mmu.pgd_phys, pgd_size)))
+ 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;
+}
+
static int rmm_check_features(void)
{
if (kvm_lpa2_is_enabled() && !rmi_has_feature(RMI_FEATURE_REGISTER_0_LPA2)) {
--
2.43.0