Re: [PATCH v2 02/18] x86/sgx: Store struct sgx_encl when allocating new VA pages

[Sean Christopherson <seanjc@google.com>]

On Fri, Dec 02, 2022, Dave Hansen wrote:
> On 12/2/22 14:35, Sean Christopherson wrote:
> >> That seems like it's going the other direction from what an OOM-kill
> >> would need to do.
> > Providing a backpointer from a VA page to its enclave allows OOM-killing the enclave
> > if its cgroup is over the limit but there are no reclaimable pages for said cgroup
> > (for SGX's definition of "reclaimable").  I.e. if all of an enclave's "regular"
> > pages have been swapped out, the only thing left resident in the EPC will be the
> > enclave's VA pages, which are not reclaimable in the kernel's current SGX
> > implementation.
> 
> Ooooooooooooooooooooh.  I'm a dummy.
> 
> 
> So, we've got a cgroup.  It's in OOM-kill mode and we're looking at the
> *cgroup* LRU lists.  We've done everything we can to the enclave and
> swapped everything out that we can.  All we're left with are these
> crummy VA pages on the LRU (or equally crummy pages).  We want to
> reclaim them but can't swap VA pages.  Our only recourse is to go to the
> enclave and kill *it*.
> 
> Right now, we can easily find an enclave's VA pages and free them.  We
> do that all the time when freeing whole enclaves.  But, what we can't
> easily do is find an enclave given a VA page.
> 
> A reverse pointer from VA page back to enclave allows the VA page's
> enclave to be located and efficiently killed.
> 
> Right?

Yep, exactly.