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

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Message-ID: <op.2cxmq7c2wjvjmi@hhuan26-mobl.amr.corp.intel.com>
Date:   Mon, 16 Oct 2023 19:10:09 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>
Cc:     "Zhang, Bo" <zhanb@...rosoft.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "yangjie@...rosoft.com" <yangjie@...rosoft.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tj@...nel.org" <tj@...nel.org>,
        "anakrish@...rosoft.com" <anakrish@...rosoft.com>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "kristen@...ux.intel.com" <kristen@...ux.intel.com>
Subject: Re: [PATCH v5 12/18] x86/sgx: Add EPC OOM path to forcefully reclaim
 EPC

On Mon, 16 Oct 2023 16:09:52 -0500, Huang, Kai <kai.huang@...el.com> wrote:
[...]

> still need to fix the bug mentioned above here.
>
> I really think you should just go this simple way:
>
> When you want to take EPC back from VM, kill the VM.
>

My only concern is that this is a compromise due to current limitation (no  
other sane way to take EPC from VMs). If we define this behavior and it  
becomes a contract to user space, then we can't change in future.

On the other hand, my understanding the reason you want this behavior is  
to enforce EPC limit at runtime. I just not sure how important it is and  
if it is a real usage given all limitations of SGX VMs we have (static EPC  
size, no migration).

Thanks

Haitao