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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 17 Dec 2018 12:10:17 -0800
Message-ID: <CALCETrX_7g+GYj2hHvFjodPw_ryrVTQdF2M3p+KYNTBUOhg-8g@mail.gmail.com>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Sean Christopherson <sean.j.christopherson@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,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
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On Mon, Dec 17, 2018 at 12:03 PM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 12/17/18 11:55 AM, Andy Lutomirski wrote:
> >> You're effectively rebuilding reverse-mapping infrastructure here.  It's
> >> a frequent thing for the core VM to need to go from 'struct page' back
> >> to the page tables mapping it.  For that we go (logically)
> >> page->{anon_vma,mapping}->vma->vm_mm->pagetable.
> > This is a bit outside my expertise here, but doesn't
> > unmap_mapping_range() do exactly what SGX wants?
>
> There's no 'struct page' for enclave memory as it stands.  That means no
> page cache, and that means there's no 'struct address_space *mapping' in
> the first place.
>
> Basically, the choice was made a long time ago to have SGX's memory
> management live outside the core VM.  I've waffled back and forth on it,
> but I do still think this is the right way to do it.

AFAICS a lack of struct page isn't a problem.  The core code seems to
understand that address_space objects might cover non-struct-page
memory.  Morally, enclave memory is a lot like hot-unpluggable PCI
space.