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Date:   Thu, 13 Jun 2019 16:48:00 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     "Xing, Cedric" <cedric.xing@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
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        "selinux@vger.kernel.org" <selinux@vger.kernel.org>,
        Jethro Beekman <jethro@fortanix.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        "Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
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        "Tricca, Philip B" <philip.b.tricca@intel.com>
Subject: Re: [RFC PATCH 2/9] x86/sgx: Do not naturally align MAP_FIXED address
Message-ID: <20190613134800.GA12791@linux.intel.com>
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On Thu, Jun 06, 2019 at 06:37:10PM +0300, Jarkko Sakkinen wrote:
> On Wed, Jun 05, 2019 at 01:14:04PM -0700, Andy Lutomirski wrote:
> > 
> > 
> > > On Jun 5, 2019, at 8:17 AM, Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> > > 
> > >> On Tue, Jun 04, 2019 at 10:10:22PM +0000, 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. 
> > > 
> > > Same semantics as with a regular mmap i.e. you can close the file and
> > > still use the mapping.
> > > 
> > > 
> > 
> > The file should be properly refcounted — vm_file should not go away while it’s mapped.

mm already takes care of that so vm_file does not go away. Still
we need an internal refcount for enclaves to synchronize with the
swapper. In summary nothing needs to be done.

> Right, makes sense. It is easy one to change essentially just removing
> internal refcount from sgx_encl and using file for the same. I'll update
> this to my tree along with the changes to remove LKM/ACPI bits ASAP.

/Jarkko