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Date:   Fri, 9 Dec 2022 08:22:26 -0800
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Subject: Re: [PATCH v2 14/18] x86/sgx: Add EPC OOM path to forcefully reclaim
 EPC
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To:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        Jarkko Sakkinen <jarkko@kernel.org>
Cc:     dave.hansen@linux.intel.com, tj@kernel.org,
        linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org,
        cgroups@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        zhiquan1.li@intel.com, Sean Christopherson <seanjc@google.com>
References: <20221202183655.3767674-1-kristen@linux.intel.com>
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 <cb5abce531c1b14118de419ba68c2a501b016873.camel@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
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On 12/9/22 08:05, Kristen Carlson Accardi wrote:
> Aside from that though, I don't think that killing enclaves makes sense
> outside the context of cgroup limits. 

I think it makes a lot of sense in theory.  Whatever situation we get
into with a cgroup's EPC we can also get into with the whole system's EPC.

*But*, it's orders of magnitude harder to hit on the whole system.
Basically, it has to be at a point where all of the EPC is consumed in
non-SGX-swappable page types like SECS or VEPC pages.  That's
_possible_, of course, but it's really hard to create because one VEPC
page can hold the info of several (32??) swapped-out EPC pages.

So, you'd need roughly 4GB of swapped-out normal enclave memory to
exhaust a system with 128MB of total enclave memory.

OOM handling *much* necessary in practice if you have a cgroup with some
modestly sized enclaves and a very tiny EPC limit.  If someone wants to
extend this OOM support to system-wide EPC later, then go ahead.  But, I
don't think it makes a lot of sense to invert this series for it.