Re: [PATCH v29 00/20] Intel SGX foundations

[Nathaniel McCallum]

On Thu, May 7, 2020 at 1:03 AM Haitao Huang
<haitao.huang@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, 06 May 2020 17:14:22 -0500, Sean Christopherson
> <sean.j.christopherson@xxxxxxxxx> 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@xxxxxxxxxx>
> >>
> >> 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.