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

[Haitao Huang]

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

> On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
> > From: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
> >
> > 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.

https://lore.kernel.org/linux-sgx/CU4H43P3H35X.1BCA3CE4D1250@seitikki/