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Date:   Tue, 11 Dec 2018 07:01:52 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     "Dr. Greg" <greg@enjellic.com>
Cc:     Josh Triplett <josh@joshtriplett.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        linux-sgx@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
        Haitao Huang <haitao.huang@linux.intel.com>,
        Jethro Beekman <jethro@fortanix.com>
Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU
Message-ID: <20181211150152.GA14731@linux.intel.com>
References: <20181210232141.5425-1-sean.j.christopherson@intel.com>
 <20181210232449.GA11843@localhost>
 <20181211145339.GA7528@wind.enjellic.com>
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On Tue, Dec 11, 2018 at 08:53:39AM -0600, Dr. Greg wrote:
> On Mon, Dec 10, 2018 at 03:24:50PM -0800, Josh Triplett wrote:
> 
> Good morning to everyone, I hope the week is progressing well.
> 
> > 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.
> 
> Sean's architecture is very simple and straight forward and thus has a
> lot going for it.
> 
> As Sean's approach indicates, by linking the exception handler to
> current->mm, SGX is very much a per memory map concept.  The issue is
> that there can be multiple enclaves loaded and excecuting in a
> processes memory map, the problem is, execution and thus exception
> handling, is very much at the per thread level.

Right, but is there a need to have a per-thread code page?  The handler
isn't per-process any more than the AEP is per-process.