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. > 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.
