On Wed, 19 May 2021 14:26:31 +0100,
Steven Price <steven.price@xxxxxxx> wrote:
>
> On 17/05/2021 18:40, Marc Zyngier wrote:
> > On Mon, 17 May 2021 13:32:37 +0100,
> > Steven Price <steven.price@xxxxxxx> 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@xxxxxxx>
> >> ---
> >> 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.
It looks that this is indeed a bug, and I'm on my way to squash it.
Can't believe we allowed that for so long...
But the architecture clearly states:
<quote>
These features are supported in AArch64 state only.
</quote>
So I'd expect something like:
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 956cdc240148..50635eacfa43 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -220,7 +220,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
switch (vcpu->arch.target) {
default:
if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
- if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
+ if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) ||
+ vcpu->kvm->arch.mte_enabled) {
ret = -EINVAL;
goto out;
}
that makes it completely impossible to create 32bit CPUs within a
MTE-enabled guest.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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