[PATCH 09/11] KVM: arm64: CCA: Prevent memslot modifications after Realm creation

[Steven Price <steven.price@arm.com>]

From: Suzuki K Poulose <suzuki.poulose@arm.com>

Once the Realm is created, prevent any changes to guest_memfd backed
memslots, as the private memory is provided by slots backed by gmem.
This will also be validated when we handle a fault for Realm Stage2 (in
a later commit).

Additionally, similar to pKVM, we do not support dirty logging or
read-only memslots.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
 arch/arm64/kvm/mmu.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 51fda7b2ff7f..eb8c5f9e9791 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2862,13 +2862,28 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	    (new->flags & (KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)))
 		return -EPERM;
 
-	if (kvm->arch.vm_flavor == VM_PROTECTED_PKVM) {
+	switch (kvm->arch.vm_flavor) {
+	case VM_PROTECTED_PKVM:
 		/* Cannot modify memslots once a pVM has run. */
 		if (pkvm_hyp_vm_is_created(kvm) &&
-		    (change == KVM_MR_DELETE || change == KVM_MR_MOVE)) {
+		    (change == KVM_MR_DELETE || change == KVM_MR_MOVE))
 			return -EPERM;
-		}
+		break;
+	case VM_REALM:
+		/*
+		 * Once the Realm is created, we cannot modify any slots that
+		 * could be providing private memory. i.e., guest_memfd backed
+		 * slots.
+		 * TODO: Handle trusted device private memory slots
+		 */
+		if (!kvm_realm_is_created(kvm))
+			break;
 
+		if (kvm_slot_has_gmem(old) || kvm_slot_has_gmem(new))
+			return -EPERM;
+		break;
+	default:
+		break;
 	}
 
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
-- 
2.43.0