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Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver
To:     Andy Lutomirski <luto@kernel.org>
Cc:     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)" 
        <linux-kernel@vger.kernel.org>
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From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <826f6a5a-fdf6-e7e5-d2d8-bcdc57c016fe@intel.com>
Date:   Mon, 17 Dec 2018 12:03:17 -0800
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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.