Re: x86/sgx: uapi change proposal

[Jarkko Sakkinen]

On Tue, Jan 08, 2019 at 07:27:11PM +0000, Huang, Kai wrote:
> > >
> > > Can one of you explain why SGX_ENCLAVE_CREATE is better than just
> > > opening a new instance of /dev/sgx for each encalve?
> > 
> > Directly associating /dev/sgx with an enclave means /dev/sgx can't be used
> > to provide ioctl()'s for other SGX-related needs, e.g. to mmap() raw EPC and
> > expose it a VM.  Proposed layout in the link below.  I'll also respond to
> > Jarkko's question about exposing EPC through /dev/sgx instead of having
> > KVM allocate it on behalf of the VM.
> > 
> > https://lkml.kernel.org/r/20181218185349.GC30082@xxxxxxxxxxxxxxx
> 
> Hi Sean,
> 
> Sorry for replying to old email. But IMHO it is not a must that Qemu needs to open some /dev/sgx and allocate/mmap EPC for guest's virtual EPC slot, instead, KVM could create private slot, which is not visible to Qemu, for virtual EPC, and KVM could call core-SGX EPC allocation API directly.
> 
> I am not sure what's the good of allowing userspace to alloc/mmap a raw EPC region? Userspace is not allowed to touch EPC anyway, expect enclave code.
> 
> To me KVM creates private EPC slot is cleaner than exposing /dev/sgx/epc and allowing userspace to map some raw EPC region. 
> 
> Thanks,
> -Kai

Side-note: this particular use case does not necessarily be solved in
the first upstream patch set, does it? Just try to keep the patch set
as small as possible (still be a huge one).

/Jarkko