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

Chao Gao
2024-04-04T01:04:04Z

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.