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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 17 Dec 2018 20:55:02 -0800
Message-ID: <CALCETrUy25OJ8Q4eH81hwtvQyLGTmYCMMkEs+m8uNWqoFVt=-g@mail.gmail.com>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>, X86 ML <x86@kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        linux-sgx@vger.kernel.org, nhorman@redhat.com,
        npmccallum@redhat.com, "Ayoun, Serge" <serge.ayoun@intel.com>,
        shay.katz-zamir@intel.com,
        Haitao Huang <haitao.huang@linux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Svahn, Kai" <kai.svahn@intel.com>, mark.shanahan@intel.com,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
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On Mon, Dec 17, 2018 at 5:39 PM Jarkko Sakkinen
<jarkko.sakkinen@linux.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.