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

Huang, Kai
2024-04-03T22:14:13Z

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?