linux-kernel - Re: [RFC PATCH 2/9] x86/sgx: Do not naturally align MAP

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Date:   Wed, 5 Jun 2019 07:08:15 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     "Xing, Cedric" <cedric.xing@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        "Tricca, Philip B" <philip.b.tricca@...el.com>
Subject: Re: [RFC PATCH 2/9] x86/sgx: Do not naturally align MAP_FIXED address

On Tue, Jun 04, 2019 at 03:10:22PM -0700, Xing, Cedric wrote:
> A bit off topic here. This mmap()/mprotect() discussion reminds me a question
> (guess for Jarkko): Now that vma->vm_file->private_data keeps a pointer to
> the enclave, why do we store it again in vma->vm_private? It isn't a big deal
> but non-NULL vm_private does prevent mprotect() from merging adjacent VMAs. 

vma->vm_ops->close also prevents merging, and we need that to refcount the
enclave and mm.

We also rely on nullifying vma->vm_private_data in the unlikely event that
adding a new mm to the enclave fails on kzalloc().