[RFC PATCH 2/9] x86/sgx: Do not naturally align MAP_FIXED address

[Jarkko Sakkinen]

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 at 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