linux-kernel - Re: [PATCH v5 09/18] x86/sgx: Store struct sgx

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Date:   Tue, 3 Oct 2023 20:07:42 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "mingo@...hat.com" <mingo@...hat.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>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "haitao.huang@...ux.intel.com" <haitao.huang@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tj@...nel.org" <tj@...nel.org>,
        "Mehta, Sohil" <sohil.mehta@...el.com>
CC:     "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "anakrish@...rosoft.com" <anakrish@...rosoft.com>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
        "yangjie@...rosoft.com" <yangjie@...rosoft.com>,
        "Zhang, Bo" <zhanb@...rosoft.com>
Subject: Re: [PATCH v5 09/18] x86/sgx: Store struct sgx_encl when allocating
 new VA pages

On Tue, 2023-10-03 at 01:45 -0500, Haitao Huang wrote:
> > 
> > Btw, probably a dumb question:
> > 
> > Theoretically if you only need to find a victim enclave you don't need  
> > to put VA
> > pages to the unreclaimable list, because those VA pages will be freed  
> > anyway
> > when enclave is killed.  So keeping VA pages in the list is for  
> > accounting all
> > the pages that the cgroup is having?
> 
> Yes basically tracking them in cgroups as they are allocated.
> 
> VAs and SECS may also come and go as swapping/unswapping happens. But if a  
> cgroup is OOM, and all reclaimables are gone (swapped out), it'd have to  
> reclaim VAs/SECs in the same cgroup starting from the front of the LRU  
> list. To reclaim a VA/SECS, it identifies the enclave from the owner of  
> the VA/SECS page and kills it, as killing enclave is the only way to  
> reclaim VA/SECS pages.

To kill enclave you just need to track SECS in  the unreclaimable list.  

Only when you want to account the total EPC pages via some list you _probably_
need to track VA as well.  But I am not quite sure about this either.