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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 17 Dec 2018 11:55:09 -0800
Message-ID: <CALCETrUhVDxMAtpyn5ahsTFwhJkzWxKa5Ur8q4FuVaKLmSyYHQ@mail.gmail.com>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        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>,
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On Mon, Dec 17, 2018 at 11:53 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 12/17/18 11:49 AM, Jarkko Sakkinen wrote:
> >> Yeah, the code is built to have one VMA and only one VMA per enclave.
> >> You need to go over the origin of this restriction and what enforces this.
> > It is before ECREATE but after that you can split it with mprotect().
> >
> > Lets take an example. I'm not sure how we would acquire mm efficiently
> > in sgx_encl_page_reclaim() otherwise than having it as a field in encl.
>
> 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?