Re: [PATCH v5 02/18] cgroup/misc: Add SGX EPC resource type and export APIs for SGX driver

Haitao Huang
2023-10-03T07:02:23Z

On Wed, 27 Sep 2023 22:59:12 -0500, Huang, Kai <kai.huang@intel.com> wrote:

> On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
>> From: Kristen Carlson Accardi <kristen@linux.intel.com>
>>
>> Add SGX EPC memory, MISC_CG_RES_SGX_EPC, to be a valid resource type
>> for the misc controller.
>>
>> Add per resource type private data so that SGX can store additional per
>> cgroup data in misc_cg->misc_cg_res[MISC_CG_RES_SGX_EPC].
>
> To be honest I don't quite understand why putting the above two changes
> in this
> patch together with exporting misc_cg_root/parent() below.
>
> Any reason why the above two cannot be done together with patch ("
> x86/sgx:
> Limit process EPC usage with misc cgroup controller"), where these
> changes are
> actually related?
>
> We all already know that a new EPC misc cgroup will be added. There's
> no need
> to actually introduce the new type here only to justify exporting some
> helper
> functions.
>

I think previous authors intended to separate all prerequisite misc
changes from SGX changes.
I can combine them if maintainers are fine with it.

>>
>> Export misc_cg_root() so the SGX driver can initialize and add those
>> additional structures to the root misc cgroup as part of initialization
>> for EPC cgroup support. This bootstraps the same additional
>> initialization for non-root cgroups in the 'alloc()' callback added in
>> the
>> previous patch.
>>
>> The SGX driver, as the EPC memory provider, will have a background
>> worker to reclaim EPC pages to make room for new allocations in the same
>> cgroup when its usage counter reaches near the limit controlled by the
>> cgroup and its ancestors. Therefore it needs to do a walk from the
>> current cgroup up to the root. To enable this walk, move parent_misc()
>> into misc_cgroup.h and make inline to make this function available to
>> SGX, rename it to misc_cg_parent(), and update kernel/cgroup/misc.c to
>> use the new name.
>
> Looks too many details in the above two paragraphs. Could we have a more
> concise justification for exporting these two functions?
>

This was added to address Jarkko's question, "why does SGX driver need to
do iterative walks?"
See: https://lore.kernel.org/all/CVHOU5G1SCUT.RCBVZ3W8G2NJ@suppilovahvero/

> And if it were me, I would put it at a relatively later position (e.g.,
> before
> the patch actually implements EPC cgroup) for better review. This also
> applies
> to the first patch.
>

I was told to move all prerequisites to the front or separate out.