On Thu, Jun 13, 2019 at 10:14:51AM -0700, Sean Christopherson wrote:

quoted

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