Re: [PATCH v5 06/18] x86/sgx: Introduce EPC page states

Haitao Huang
2023-10-03T04:49:51Z

On Wed, 27 Sep 2023 05:28:36 -0500, Huang, Kai <kai.huang@intel.com> wrote:

> On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
>> Use the lower 3 bits in the flags field of sgx_epc_page struct to
>> track EPC states in its life cycle and define an enum for possible
>> states. More state(s) will be added later.
>
> This patch does more than what the changelog claims to do. AFAICT it
> does
> below:
>
> 1) Use the lower 3 bits to track EPC page status
> 2) Rename SGX_EPC_PAGE_RECLAIMER_TRACKED to SGX_EPC_PAGE_RERCLAIMABLE
> 3) Introduce a new state SGX_EPC_PAGE_UNRECLAIMABLE
> 4) Track SECS and VA pages as SGX_EPC_PAGE_UNRECLAIMABLE
>
> The changelog only says 1) IIUC.
>
I don't quite get why you would view 3) as a separate item from 1).
In my view, 4) is not done as long as there is not separate list to track
it.
Maybe I should make it clear the "states" vs "tracking". States are just
bits in the flags, "tracking" is done using the lists by ksgxd/cgroup. And
this patch is really about "states"
Would that clarify the intention of the patch?

> If we really want to do all these in one patch, then the changelog
> should at
> least mention the justification of all of them.
>
> But I don't see why 3) and 4) need to be done here. Instead, IMHO they
> should
> be done in a separate patch, and do it after the unreclaimable list is
> introduced (or you need to bring that patch forward).
>
>
> For instance, ...
>
> [snip]
>
>> +
>> + /* Page is in use but tracked in an unreclaimable LRU list. These are
>> + * only reclaimable when the whole enclave is OOM killed or the
>> enclave
>> + * is released, e.g., VA, SECS pages
>> + * Becomes NOT_TRACKED after sgx_drop_epc()
>> + */
>> + SGX_EPC_PAGE_UNRECLAIMABLE = 3,
>
> ... We even don't have the unreclaimable LRU list yet. It's odd to have
> this
> comment here.
>

Yeah, I should take out the mentioning of the LRUs from definitions of the
states.

Thanks
Haitao