Re: [PATCH v16 17/45] KVM: arm64: CCA: Tear down RTTs

On 04/08/2026 13:16, Suzuki K Poulose wrote:
> Hi there
> 
> On 03/08/2026 23:29, Alper Gun wrote:
>> On Mon, Aug 3, 2026 at 6:45 AM Steven Price <[email protected]> wrote:
>>> [...]
>>> +static void realm_unmap_stage2(struct kvm *kvm)
>>> +{
>>> +       struct realm *realm = &kvm->arch.realm;
>>> +
>>> +       lockdep_assert_held(&kvm->arch.config_lock);
>>> +
>>> +       if (realm->stage2_unmapped)
>>> +               return;
>>> +
>>> +       write_lock(&kvm->mmu_lock);
>>> +       kvm_stage2_unmap_range(&kvm->arch.mmu, 0,
>>> +                              BIT(realm->ia_bits - 1), true);
>>> +       write_unlock(&kvm->mmu_lock);
>>> +
>>> +       realm->stage2_unmapped = true;
>>> +}
>>> +
>>> +int kvm_realm_teardown_stage2(struct kvm *kvm)
>>> +{
>>> +       lockdep_assert_held(&kvm->arch.config_lock);
>>> +
>>> +       realm_unmap_stage2(kvm);
>>> +       return realm_destroy_rtts(kvm);
>>> +}
>>
>> Hi Steven,
>>
>> I noticed a warning in dmesg when destroying a realm:
>>
>>    [  158.533495] Call trace:
>>    [  158.535927]  kvm_destroy_realm+0x208/0x218
>>    [  158.540356]  kvm_arch_destroy_vm+0xc8/0xd8
>>    [  158.544439]  kvm_put_kvm+0x324/0x4b0
>>    [  158.548002]  kvm_vm_stats_release+0x1c/0x38
> 
> Thanks for the report and the detailed analysis.
> 
>>
>> I traced this and found the following:
>>
>> At this point, calling realm_destroy_rtts() may fail destroying the RTTs
>> because RECs are still active and the Realm is not terminated, but the

May be we should bail out early in the realm_map_ipa() based on the
state of the Realm (i.e. state != ACTIVE). But looking at this
I see that we serialize the state of the realm using the config_lock,
which is a bit odd.

>> walk finishes and still sets realm->rtts_destroyed = true.
>>
>> Later, kvm_destroy_realm() calls rmi_realm_terminate() and then calls
>> realm_destroy_rtts(kvm) again. But because realm->rtts_destroyed is 
>> already
>> set to true, it exits early without tearing down the RTTs.
>>
>> Consequently, rmi_realm_destroy() is invoked while the RTT tables still
>> exist in RMM, which fails and triggers WARN_ON(rmi_realm_destroy).
>>
>> The fix I used was to remove realm_destroy_rtts() from
>> kvm_realm_teardown_stage2():
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -434,7 +434,7 @@ int kvm_realm_teardown_stage2(struct kvm *kvm)
>>    lockdep_assert_held(&kvm->arch.config_lock);
>>
>>    realm_unmap_stage2(kvm);
>> - return realm_destroy_rtts(kvm);
>> + return 0;
>>   }
>>
>> I think we don't need RTT destruction here as it will be handled 
>> cleanly in
>> kvm_destroy_realm() later.
> 
> That sounds sensible to me, I will take a look and fix it locally for 
> the next version.

On a second look, I think the rtts_destroyed flag may not be saving us
much. If the RTTs are destroyed, we should complete the second round
fairly easily.

Suzuki

> 
> 
> Thanks
> Suzuki
> 
>>
>> Thanks,
>> Alper
>