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

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Date:   Thu, 10 Jan 2019 19:43:33 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jethro Beekman <jethro@...tanix.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

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@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

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