linux-kernel - Re: [PATCH v2 14/18] x86/sgx: Add EPC OOM path to forcefully reclaim EPC

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Message-ID: <e5aff02b-713c-ccd8-7211-d07ff6d7adb2@intel.com>
Date:   Fri, 9 Dec 2022 08:22:26 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     dave.hansen@...ux.intel.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        zhiquan1.li@...el.com, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 14/18] x86/sgx: Add EPC OOM path to forcefully reclaim
 EPC

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.