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From:   "Huang, Kai" <kai.huang@intel.com>
To:     "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        "Andy Lutomirski" <luto@kernel.org>
CC:     Jethro Beekman <jethro@fortanix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "x86@kernel.org" <x86@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Haitao Huang <haitao.huang@linux.intel.com>,
        "Dr . Greg Wettstein" <greg@enjellic.com>
Subject: RE: x86/sgx: uapi change proposal
Thread-Topic: x86/sgx: uapi change proposal
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Date:   Tue, 8 Jan 2019 19:27:11 +0000
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> >
> > 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@linux.intel.com

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