On Thu, Nov 04, 2021 at 08:29:49AM -0700, Dave Hansen wrote: > On 11/4/21 8:25 AM, Jarkko Sakkinen wrote: > > 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? > > I don't think so, but there's nothing stopping us from doing it ourselves. Ok. > > It should be fairly effecient just to check the pages by using > > encl->page_tree. > > That sounds more complicated and slower than what I suggested. You > could even just check the refcount on the page. I _think_ page cache > pages have a refcount of 2. So, look for the refcount that means "no > more PCMD in this page", and just free it if so. Umh, so... there is total 32 PCMD's per one page. /Jarkko
