On 17/05/2021 18:40, Marc Zyngier wrote:

On Mon, 17 May 2021 13:32:37 +0100,
Steven Price [off-list ref] wrote:

quoted

It's now safe for the VMM to enable MTE in a guest, so expose the
capability to user space.

Signed-off-by: Steven Price <steven.price@arm.com>
---
 arch/arm64/kvm/arm.c      | 9 +++++++++
 arch/arm64/kvm/sys_regs.c | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 1cb39c0803a4..e89a5e275e25 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c

@@ -93,6 +93,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		r = 0;
 		kvm->arch.return_nisv_io_abort_to_user = true;
 		break;
+	case KVM_CAP_ARM_MTE:
+		if (!system_supports_mte() || kvm->created_vcpus)
+			return -EINVAL;
+		r = 0;
+		kvm->arch.mte_enabled = true;

As far as I can tell from the architecture, this isn't valid for a
32bit guest.

Indeed, however the MTE flag is a property of the VM not of the vCPU.
And, unless I'm mistaken, it's technically possible to create a VM where
some CPUs are 32 bit and some 64 bit. Not that I can see much use of a
configuration like that.

Steve

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