linux-kernel - RE: x86/sgx: uapi change proposal

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Date:   Tue, 8 Jan 2019 19:27:11 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "Andy Lutomirski" <luto@...nel.org>
CC:     Jethro Beekman <jethro@...tanix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: RE: x86/sgx: uapi change proposal

> >
> > 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