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

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Date:   Mon, 02 Oct 2023 23:49:42 -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 06/18] x86/sgx: Introduce EPC page states

On Wed, 27 Sep 2023 05:28:36 -0500, Huang, Kai <kai.huang@...el.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