Re: [PATCH v12 6/8] arm64: kvm: Expose KVM_ARM_CAP_MTE

[Steven Price]

On 17/05/2021 18:40, Marc Zyngier wrote:
> On Mon, 17 May 2021 13:32:37 +0100,
> Steven Price <steven.price@arm.com> wrote:
>>
>> 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