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

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Message-ID: <7a1a5125-9da2-47b6-ba0f-cf24d84df16b@intel.com>
Date:   Wed, 18 Oct 2023 08:37:25 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Haitao Huang <haitao.huang@...ux.intel.com>,
        Michal Koutný <mkoutny@...e.com>
Cc:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "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 10/18/23 08:26, Haitao Huang wrote:
> Maybe not in sense of killing something. My understanding memory.reclaim
> does not necessarily invoke the OOM killer. But what I really intend to
> say is we can have a separate knob for user to express the need for
> reducing the current usage explicitly and keep "misc.max' non-preemptive
> semantics intact. When we implement that new knob, then we can define
> what kind of reclaim for that. Depending on vEPC implementation, it may
> or may not involve killing VMs. But at least that semantics will be
> explicit for user.

I'm really worried that you're going for "perfect" semantics here.  This
is SGX.  It's *NOT* getting heavy use and even fewer folks will ever
apply cgroup controls to it.

Can we please stick to simple, easily-coded rules here?  I honestly
don't think these corner cases matter all that much and there's been
*WAY* too much traffic in this thread for what is ultimately not that
complicated.  Focus on *ONE* thing:

1. Admin sets a limit
2. Enclave is created
3. Enclave hits limit, allocation fails

Nothing else matters.  What if the admin lowers the limit on an
already-created enclave?  Nobody cares.  Seriously.  What about inducing
reclaim?  Nobody cares.  What about vEPC?  Doesn't matter, an enclave
page is an enclave page.