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

[Huang, Kai]

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.