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Date:   Fri, 21 Dec 2018 08:28:25 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     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
Message-ID: <20181221162825.GB26865@linux.intel.com>
References: <20181214215729.4221-1-sean.j.christopherson@intel.com>
 <7706b2aa71312e1f0009958bcab24e1e9d8d1237.camel@linux.intel.com>
 <598cd050-f0b5-d18c-96a0-915f02525e3e@fortanix.com>
 <20181219091148.GA5121@linux.intel.com>
 <613c6814-4e71-38e5-444a-545f0e286df8@fortanix.com>
 <20181219144515.GA30909@linux.intel.com>
 <CALCETrW_8LnitFamYUU7POHFOJFxLO7ESFUdS=aeG_SOvHVPkw@mail.gmail.com>
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On Wed, Dec 19, 2018 at 06:58:48PM -0800, Andy Lutomirski wrote:
> > On Dec 19, 2018, at 6:45 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> >
> >> On Wed, Dec 19, 2018 at 09:36:16AM +0000, Jethro Beekman wrote:
> 
> > I agree with Jethro, passing the enclave_fd as a param is obnoxious.
> > And it means the user needs to open /dev/sgx to do anything with an
> > enclave fd, e.g. the enclave fd might be passed to a builder thread,
> > it shouldn't also need the device fd.
> >
> > E.g.:
> >
> >    sgx_fd = open("/dev/sgx", O_RDWR);
> >    BUG_ON(sgx_fd < 0);
> >
> >    enclave_fd = ioctl(sgx_fd, SGX_ENCLAVE_CREATE, &ecreate);
> >    BUG_ON(enclave_fd < 0);
> >
> >    ret = ioctl(enclave_fd, SGX_ENCLAVE_ADD_PAGE, &eadd);
> >    BUG_ON(ret);
> >
> >    ...
> >
> >    ret = ioctl(enclave_fd, SGX_ENCLAVE_INIT, &einit);
> >    BUG_ON(ret);
> >
> >    ...
> >
> >    close(enclave_fd);
> >    close(sgx_fd);
> >
> >
> > Take a look at virt/kvm/kvm_main.c to see how KVM manages anon inodes
> > and ioctls for VMs and vCPUs.
> 
> 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