Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

Huang, Kai
2024-04-04T01:25:12Z

On 4/04/2024 2:03 pm, Chao Gao wrote:
> On Thu, Apr 04, 2024 at 11:13:49AM +1300, Huang, Kai wrote:
>>
>>
>> On 22/03/2024 3:17 am, Yamahata, Isaku wrote:
>>>>> +
>>>>> + for_each_online_cpu(i) {
>>>>> + int pkg = topology_physical_package_id(i);
>>>>> +
>>>>> + if (cpumask_test_and_set_cpu(pkg, packages))
>>>>> + continue;
>>>>> +
>>>>> + /*
>>>>> + * Program the memory controller in the package with an
>>>>> + * encryption key associated to a TDX private host key id
>>>>> + * assigned to this TDR. Concurrent operations on same memory
>>>>> + * controller results in TDX_OPERAND_BUSY. Avoid this race by
>>>>> + * mutex.
>>>>> + */
>>>>> + mutex_lock(&tdx_mng_key_config_lock[pkg]);
>>>> the lock is superfluous to me. with cpu lock held, even if multiple CPUs try to
>>>> create TDs, the same set of CPUs (the first online CPU of each package) will be
>>>> selected to configure the key because of the cpumask_test_and_set_cpu() above.
>>>> it means, we never have two CPUs in the same socket trying to program the key,
>>>> i.e., no concurrent calls.
>>> Makes sense. Will drop the lock.
>>
>> Hmm.. Skipping in cpumask_test_and_set_cpu() would result in the second
>> TDH.MNG.KEY.CONFIG not being done for the second VM. No?
>
> No. Because @packages isn't shared between VMs.

I see. Thanks.