Re: [PATCH v5 12/18] x86/sgx: Add EPC OOM path to forcefully reclaim EPC

[Haitao Huang]

On Mon, 09 Oct 2023 21:12:27 -0500, Huang, Kai <kai.huang@xxxxxxxxx> wrote:

> > > > >
> > > > Later the hosting process could migrated/reassigned to another  
> > cgroup?
> > > > What to do when the new cgroup is OOM?
> > > >
> > >
> > > You addressed in the documentation, no?
> > >
> > > +Migration
> > > +---------
> > > +
> > > +Once an EPC page is charged to a cgroup (during allocation), it
> > > +remains charged to the original cgroup until the page is released
> > > +or reclaimed.  Migrating a process to a different cgroup doesn't
> > > +move the EPC charges that it incurred while in the previous cgroup
> > > +to its new cgroup.
> >
> > Should we kill the enclave though because some VA pages may be in the  
> > new
> > group?
>
> I guess acceptable?
>
> And any difference if you keep VA/SECS to unreclaimabe list?

Tracking VA/SECS allows all cgroups, in which an enclave has allocation,  
to identify the enclave following the back pointer and kill it as needed.

> If you migrate one
> enclave to another cgroup, the old EPC pages stay in the old cgroup  
> while the
> new one is charged to the new group IIUC.
>
> I am not cgroup expert, but by searching some old thread it appears this  
> isn't a
> supported model:
>
> https://lore.kernel.org/lkml/YEyR9181Qgzt+Ps9@xxxxxxxxxxxxxxx/

IIUC it's a different problem here. If we don't track the allocated VAs in  
the new group, then the enclave that spans the two groups can't be killed  
by the new group. If so, some enclave could just hide in some small group  
and never gets killed but keeps allocating in a different group?

Thanks
Haitao