linux-kernel - Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

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Date:   Tue, 18 Dec 2018 15:18:53 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...el.com>, X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, nhorman@...hat.com,
        npmccallum@...hat.com, "Ayoun, Serge" <serge.ayoun@...el.com>,
        shay.katz-zamir@...el.com,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, mark.shanahan@...el.com,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

On Mon, Dec 17, 2018 at 08:55:02PM -0800, Andy Lutomirski wrote:
> On Mon, Dec 17, 2018 at 5:39 PM Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> >
> > On Mon, Dec 17, 2018 at 02:20:48PM -0800, Sean Christopherson wrote:
> > > The only potential hiccup I can see is the build flow.  Currently,
> > > EADD+EEXTEND is done via a work queue to avoid major performance issues
> > > (10x regression) when userspace is building multiple enclaves in parallel
> > > using goroutines to wrap Cgo (the issue might apply to any M:N scheduler,
> > > but I've only confirmed the Golang case).  The issue is that allocating
> > > an EPC page acts like a blocking syscall when the EPC is under pressure,
> > > i.e. an EPC page isn't immediately available.  This causes Go's scheduler
> > > to thrash and tank performance[1].
> >
> > I don't see any major issues having that kthread. All the code that
> > maps the enclave would be removed.
> >
> > I would only allow to map enclave to process address space after the
> > enclave has been initialized i.e. SGX_IOC_ENCLAVE_ATTACH.
> >
> 
> What's SGX_IOC_ENCLAVE_ATTACH?  Why would it be needed at all?  I
> would imagine that all pages would be faulted in as needed (or
> prefaulted as an optimization) and the enclave would just work in any
> process.

The way I see it the efficient way to implement this is to have the
enclave attached to a single process address space at a time.

#PF handler is trivial with multiple address spaces but swapping is
a bit tedious as you would need to zap N processes.

/Jarkko