linux-kernel - Re: [PATCH v16 18/22] platform/x86: Intel SGX driver

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Message-ID: <20181108144603.GA14072@linux.intel.com>
Date:   Thu, 8 Nov 2018 16:46:03 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org, dave.hansen@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...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 v16 18/22] platform/x86: Intel SGX driver

On Wed, Nov 07, 2018 at 10:00:57AM -0800, Sean Christopherson wrote:
> What do we gain by a single buffer vs. separate buffers?  The ioctl()
> would be slightly smaller but it seems like the actual code would be
> more complex.

I'm fine with either. It was just a suggestion.

> The enclave build process also utilizes the backing as temp storage
> to avoid having to alloc kernel memory when queueing pages to be added
> by the worker thread (which reminds me that I wanted to document why a
> worker thread is used).  Keeping this behavior would effectively make
> providing backing mandatory.

Would it be a problem just allocate those pages with alloc_page() and
free them in the worker thread?

> Are there any potential complications with ENCLS consuming userspace
> pointers?  We'd have to wrap them with user_access_{begin,end}() and
> probably tweak the fixup, but I assume having the fixup handler means
> we're generally ok?

Last time I did it I used get_user_pages() for pinning. I'm not sure
why I should do anything but just re-use that.

/Jarkko