Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 11 Dec 2018 10:40:56 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Josh Triplett <josh@joshtriplett.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        X86 ML <x86@kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-sgx@vger.kernel.org,
        Haitao Huang <haitao.huang@linux.intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
        "Dr. Greg Wettstein" <greg@enjellic.com>
Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU
Message-ID: <20181211184056.GF14731@linux.intel.com>
References: <20181210232141.5425-1-sean.j.christopherson@intel.com>
 <20181210232449.GA11843@localhost>
 <EEE078E7-7F37-4F74-8874-46E16C1E0A77@amacapital.net>
 <20181211165253.GB14731@linux.intel.com>
 <CALCETrXOXh8Gb_d7NYLakx4w+JVEe79t11wFPLpy+5MEq9kq=A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALCETrXOXh8Gb_d7NYLakx4w+JVEe79t11wFPLpy+5MEq9kq=A@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Dec 11, 2018 at 09:58:19AM -0800, Andy Lutomirski wrote:
> > On Dec 11, 2018, at 8:52 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> >
> >> On Tue, Dec 11, 2018 at 07:41:27AM -0800, Andy Lutomirski wrote:
> >>
> >>
> >>>> On Dec 10, 2018, at 3:24 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> >>>>
> >>>> On Mon, Dec 10, 2018 at 03:21:37PM -0800, Sean Christopherson wrote:
> >>>> At that point I realized it's a hell of a lot easier to simply provide
> >>>> an IOCTL via /dev/sgx that allows userspace to register a per-process
> >>>> ENCLU exception handler.  At a high level, the basic idea is the same
> >>>> as the vDSO approach: provide a hardcoded fixup handler for ENCLU and
> >>>> attempt to fixup select unhandled exceptions that occurred in user code.
> >>>
> >>> So, on the one hand, this is *absolutely* much cleaner than the VDSO
> >>> approach. On the other hand, this is global process state and has some
> >>> of the same problems as a signal handler as a result.
> >>
> >> I liked the old version better for this reason
> >
> > This isn't fundamentally different than forcing all EENTER calls through
> > the vDSO, which is also per-process.  Technically this is more flexible
> > in that regard since userspace gets to choose where their one ENCLU gets
> > to reside.  Userspace can have per-enclave entry flows so long as the
> > actual ENLU[EENTER] is common, same as vDSO.
> 
> Right. The problem is that user libraries have a remarkably hard time
> agreeing on where their one copy of anything lives.

Ah, so vDSO is the mean parent that takes away their kids' toys because
thay haven't learned to share :)