On Wed, 27 Sep 2023 06:35:57 -0500, Huang, Kai <kai.hu...@intel.com> wrote:

On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
From: Sean Christopherson <sean.j.christopher...@intel.com>

In a later patch, when a cgroup has exceeded the max capacity for EPC
pages, it may need to identify and OOM kill a less active enclave to
make room for other enclaves within the same group. Such a victim
enclave would have no active pages other than the unreclaimable Version
Array (VA) and SECS pages.

What does "no active pages" mean?

EPC pages in use.

A "less active enclave" doesn't necessarily mean it has "no active pages"?

I'll rephrase the above sentences

Therefore, the cgroup needs examine its
                        needs to

unreclaimable page list, and finding an enclave given a SECS page or a

VA page. This will require a backpointer from a page to an enclave,
which is not available for VA pages.

Because struct sgx_epc_page instances of VA pages are not owned by an
sgx_encl_page instance, mark their owner as sgx_encl: pass the struct
sgx_encl of the enclave allocating the VA page to sgx_alloc_epc_page(),
which will store this value in the owner field of the struct

IMHO this paragraph is hard to understand and can be more concise:

One VA page can be shared by multiple enclave pages thus cannot be associated with any 'struct sgx_encl_page' instance. Set the owner of VA page to the
enclave instead.


In a later patch, VA pages will be placed in an
unreclaimable queue that can be examined by the cgroup to select the OOM
killed enclave.

The code to "place the VA page to unreclaimable queue" has been done in earlier patch ("x86/sgx: Introduce EPC page states"). Just the unreclaimable list isn't introduced yet. I think you should just introduce it first then you can get rid
of those "in a later patch" staff.

I hope I was able to clarify to you in other threads that VA pages are not placed in any queue/list until [PATCH v5 11/18] x86/sgx: store unreclaimable pages in LRU lists.

This patch is the first one to implement tracking for unreclaimable pages. I'll add that as a transition hint.

And nit: please use "unreclaimable list" consistently (not queue).

Yes will do

Btw, probably a dumb question:

Theoretically if you only need to find a victim enclave you don't need to put VA pages to the unreclaimable list, because those VA pages will be freed anyway when enclave is killed. So keeping VA pages in the list is for accounting all
the pages that the cgroup is having?

Yes basically tracking them in cgroups as they are allocated.

VAs and SECS may also come and go as swapping/unswapping happens. But if a cgroup is OOM, and all reclaimables are gone (swapped out), it'd have to reclaim VAs/SECs in the same cgroup starting from the front of the LRU list. To reclaim a VA/SECS, it identifies the enclave from the owner of the VA/SECS page and kills it, as killing enclave is the only way to reclaim VA/SECS pages.

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