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

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Message-ID: <8593359034d9173be5efd9c055ea782e44fbcdad.camel@intel.com>
Date:   Wed, 11 Oct 2023 00:31:19 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Mehta, Sohil" <sohil.mehta@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tj@...nel.org" <tj@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "haitao.huang@...ux.intel.com" <haitao.huang@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "yangjie@...rosoft.com" <yangjie@...rosoft.com>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
        "Zhang, Bo" <zhanb@...rosoft.com>,
        "anakrish@...rosoft.com" <anakrish@...rosoft.com>
Subject: Re: [PATCH v5 12/18] x86/sgx: Add EPC OOM path to forcefully reclaim
 EPC

On Tue, 2023-10-10 at 12:05 -0500, Haitao Huang wrote:
> On Mon, 09 Oct 2023 21:12:27 -0500, Huang, Kai <kai.huang@...el.com> 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@mtj.duckdns.org/
> > 
> 
> 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?
> 

I mean from the link above IIUC migrating enclave among different cgroups simply
isn't a supported model, thus any bad behaviour isn't a big concern in terms of
decision making.