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From:   Nathaniel McCallum <npmccallum@redhat.com>
Date:   Thu, 7 May 2020 12:49:15 -0400
Message-ID: <CAOASepNVckens=wiWpHj291EAo0ndi7GCVHd9j7BPn8rjy7Ykg@mail.gmail.com>
Subject: Re: [PATCH v29 00/20] Intel SGX foundations
To:     Haitao Huang <haitao.huang@linux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
        dave.hansen@intel.com, Neil Horman <nhorman@redhat.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        andriy.shevchenko@linux.intel.com, tglx@linutronix.de,
        "Svahn, Kai" <kai.svahn@intel.com>, bp@alien8.de,
        Josh Triplett <josh@joshtriplett.org>, luto@kernel.org,
        kai.huang@intel.com, David Rientjes <rientjes@google.com>,
        "Xing, Cedric" <cedric.xing@intel.com>,
        Patrick Uiterwijk <puiterwijk@redhat.com>
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On Thu, May 7, 2020 at 1:03 AM Haitao Huang
<haitao.huang@linux.intel.com> wrote:
>
> On Wed, 06 May 2020 17:14:22 -0500, Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
>
> > On Wed, May 06, 2020 at 05:42:42PM -0400, Nathaniel McCallum wrote:
> >> Tested on Enarx. This requires a patch[0] for v29 support.
> >>
> >> Tested-by: Nathaniel McCallum <npmccallum@redhat.com>
> >>
> >> However, we did uncover a small usability issue. See below.
> >>
> >> [0]:
> >> https://github.com/enarx/enarx/pull/507/commits/80da2352aba46aa7bc6b4d1fccf20fe1bda58662
> >
> > ...
> >
> >> > * Disallow mmap(PROT_NONE) from /dev/sgx. Any mapping (e.g.
> >> anonymous) can
> >> >   be used to reserve the address range. Now /dev/sgx supports only
> >> opaque
> >> >   mappings to the (initialized) enclave data.
> >>
> >> The statement "Any mapping..." isn't actually true.
> >>
> >> Enarx creates a large enclave (currently 64GiB). This worked when we
> >> created a file-backed mapping on /dev/sgx/enclave. However, switching
> >> to an anonymous mapping fails with ENOMEM. We suspect this is because
> >> the kernel attempts to allocate all the pages and zero them but there
> >> is insufficient RAM available. We currently work around this by
> >> creating a shared mapping on /dev/zero.
> >
> > Hmm, the kernel shouldn't actually allocate physical pages unless they're
> > written.  I'll see if I can reproduce.
> >
>
> For larger size mmap, I think it requires enabling vm overcommit mode 1:
> echo 1 | sudo tee /proc/sys/vm/overcommit_memory

Which means the default experience isn't good.