[PATCH v10 33/43] arm64: RME: Hide KVM_CAP_READONLY_MEM for realm guests

Steven Price
2025-08-20T14:59:52Z

For protected memory read only isn't supported by the RMM. While it may
be possible to support read only for unprotected memory, this isn't
supported at the present time.

Note that this does mean that ROM (or flash) data cannot be emulated
correctly by the VMM as the stage 2 mappings are either always
read/write or are trapped as MMIO (so don't support operations where the
syndrome information doesn't allow emulation, e.g. load/store pair).

This restriction can be lifted in the future by allowing the unprotected
stage 2 mappings to be made read only.

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 since v7:
* Updated commit message to spell out the impact on ROM/flash
emulation.
---
arch/arm64/kvm/arm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a090e9a74b46..23e87076330e 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -341,7 +341,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ONE_REG:
case KVM_CAP_ARM_PSCI:
case KVM_CAP_ARM_PSCI_0_2:
- case KVM_CAP_READONLY_MEM:
case KVM_CAP_MP_STATE:
case KVM_CAP_IMMEDIATE_EXIT:
case KVM_CAP_VCPU_EVENTS:
@@ -356,6 +355,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = 1;
break;
case KVM_CAP_COUNTER_OFFSET:
+ case KVM_CAP_READONLY_MEM:
case KVM_CAP_SET_GUEST_DEBUG:
r = !kvm_is_realm(kvm);
break;
--
2.43.0