Re: [PATCH] x86/sgx: Free backing memory after faulting the enclave page

[Jarkko Sakkinen]

On Thu, 2021-11-04 at 08:13 -0700, Dave Hansen wrote:
> On 11/4/21 8:04 AM, Jarkko Sakkinen wrote:
> > > Do we also need to deal with truncating the PCMD?  (For those watching
> > > along at home, there are two things SGX swaps to RAM: the actual page
> > > data and also some metadata that ensures page integrity and helps
> > > prevent things like rolling back to old versions of swapped pages)
> > Yes.
> > 
> > This can be achieved by iterating through all of the enclave pages,
> > which share the same shmem page for storing their PCMD's, as the one
> > being faulted back. If none of those pages is swapped, the PCMD page can
> > safely truncated.
> 
> I was thinking we could just read the page.  If it's all 0's, truncate it.

Hmm... did ELDU zero PCMD as a side-effect?

It should be fairly effecient just to check the pages by using
encl->page_tree.

/Jarkko