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

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Date:   Tue, 03 Oct 2023 02:00:04 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "hpa@...or.com" <hpa@...or.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Huang, Kai" <kai.huang@...el.com>
Cc:     "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "yangjie@...rosoft.com" <yangjie@...rosoft.com>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
        "Zhang, Bo" <zhanb@...rosoft.com>,
        "anakrish@...rosoft.com" <anakrish@...rosoft.com>
Subject: Re: [PATCH v5 02/18] cgroup/misc: Add SGX EPC resource type and
 export APIs for SGX driver

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

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

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