[PATCH v10 30/43] arm64: RME: Prevent Device mappings for Realms

Steven Price
2025-08-20T14:59:39Z

Physical device assignment is not yet supported by the RMM, so it
doesn't make much sense to allow device mappings within the realm.
Prevent them when the guest is a realm.

Signed-off-by: Steven Price <steven.price@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes from v6:
* Fix the check in user_mem_abort() to prevent all pages that are not
guest_memfd() from being mapped into the protected half of the IPA.
Changes from v5:
* Also prevent accesses in user_mem_abort()
---
arch/arm64/kvm/mmu.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 676c01d80875..0a0426eece87 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1184,6 +1184,10 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
if (is_protected_kvm_enabled())
return -EPERM;

+ /* We don't support mapping special pages into a Realm */
+ if (kvm_is_realm(kvm))
+ return -EPERM;
+
size += offset_in_page(guest_ipa);
guest_ipa &= PAGE_MASK;

@@ -1821,6 +1825,15 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (exec_fault && s2_force_noncacheable)
return -ENOEXEC;

+ /*
+ * For now we shouldn't be hitting protected addresses because they are
+ * handled in private_memslot_fault(). In the future this check may be
+ * relaxed to support e.g. protected devices.
+ */
+ if (vcpu_is_rec(vcpu) &&
+ kvm_gpa_from_fault(kvm, fault_ipa) == fault_ipa)
+ return -EINVAL;
+
/*
* Potentially reduce shadow S2 permissions to match the guest's own
* S2. For exec faults, we'd only reach this point if the guest
--
2.43.0