[PATCH v13 32/48] arm64: Don't expose stolen time for realm guests

Steven Price
2026-03-18T15:56:22Z

It doesn't make much sense as a realm guest wouldn't want to trust the
host. It will also need some extra work to ensure that KVM will only
attempt to write into a shared memory region. So for now just disable
it.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v7:
* Update the documentation to add a note about stolen time being
unavailable in a realm.
---
Documentation/virt/kvm/api.rst | 3 +++
arch/arm64/kvm/arm.c | 5 ++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bc180c853faf..70911fe6d435 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -9240,6 +9240,9 @@ is supported, than the other should as well and vice versa. For arm64
see Documentation/virt/kvm/devices/vcpu.rst "KVM_ARM_VCPU_PVTIME_CTRL".
For x86 see Documentation/virt/kvm/x86/msr.rst "MSR_KVM_STEAL_TIME".

+Note that steal time accounting is not available when a guest is running
+within a Arm CCA realm (machine type KVM_VM_TYPE_ARM_REALM).
+
8.25 KVM_CAP_S390_DIAG318
-------------------------

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 61182eb0cf70..7d92ddb06460 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -469,7 +469,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = system_supports_mte();
break;
case KVM_CAP_STEAL_TIME:
- r = kvm_arm_pvtime_supported();
+ if (kvm_is_realm(kvm))
+ r = 0;
+ else
+ r = kvm_arm_pvtime_supported();
break;
case KVM_CAP_ARM_EL1_32BIT:
r = cpus_have_final_cap(ARM64_HAS_32BIT_EL1);
--
2.43.0