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

[Jarkko Sakkinen]

On Thu, Jun 13, 2019 at 10:14:51AM -0700, Sean Christopherson wrote:
> > I don't get this. The swapper takes a read lock on mm->mmap_sem, which locks
> > the vma, which in turn reference counts vma->vm_file. Why is the internal
> > refcount still needed? 
> 
> mmap_sem is only held when reclaim is touching PTEs, e.g. to test/clear
> its accessed bit and to zap the PTE.  The liveliness of the enclave needs
> to be guaranteed for the entire duration of reclaim, e.g. we can't have
> the enclave disappearing when we go to do EWB.  It's also worth nothing
> that a single reclaim may operate on more than one mmap_sem, as enclaves
> can be shared across processes (mm_structs).

Anyway, the takeaway I got from this is that encl->refcount does not
need to be updated for VMAs (sent a patch to linux-sgx that I plan
merge).

/Jarkko