linux-kernel - Re: [PATCH 2/2] selftests/sgx: Add SGX selftest augment_via_eaccept

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Date:   Wed, 17 Aug 2022 08:43:57 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     "Dhanraj, Vijay" <vijay.dhanraj@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] selftests/sgx: Add SGX selftest
 augment_via_eaccept_long

Hi Jarkko,

On 8/17/2022 7:53 AM, Jarkko Sakkinen wrote:
> On Wed, Aug 17, 2022 at 05:44:31PM +0300, Jarkko Sakkinen wrote:
>> On Tue, Aug 16, 2022 at 09:35:27PM -0700, Reinette Chatre wrote:
>>>>>> This portion below was also copied from previous test and by only
>>>>>> testing a write to the first page of the range the purpose is not
>>>>>> clear. Could you please elaborate if the intention is to only test
>>>>>> accessibility of the first page and why that is sufficient?
>>>>>
>>>>> It is sufficient because the test reproduces the bug. It would have to be
>>>>> rather elaborated why you would possibly want to do more than that.
>>>
>>> That is fair. An accurate comment (currently an inaccurate copy&paste) would
>>> help to explain this part of the test.
>>
>> I would simply add something like:
>>
>> /* 
>>  * Define memory pool size big enough to trigger the reclaimer in the EAUG
>>  * path of the page reclaimer.
>>  */
>>
>> Suggestions/edits obviously welcome for the comment.

The comment seems to better match the code below than the area referred to above:
        static const unsigned long edmm_size = 8589934592; //8G

Even so, I think that raises the point that this is platform specific since
edmm_size of 8GB would not trigger reclaimer on all platforms.

How about adjusting it to:
/*
 * Define memory pool size big enough to trigger the reclaimer in the EAUG
 * path of the page reclaimer on some platforms. This constant has been
 * successful in triggering a bug on some platforms (independent of the
 * platforms where the reclaimer is triggered) and thus considered
 * appropriate for general use.
 */ 


Regarding the area referred to above, a comment like below may help:

/*
 * Pool of pages were successfully added to enclave. Perform sanity
 * check on first page of the pool only to ensure data can be written
 * to and read from a dynamically added enclave page.
 */

> 
> I wonder if we could put .bt files somewhere to make them available. In
> root causing this bug bpftrace scripting was the key so it would nice to
> have them available along with kselftest.
> 
> I could imagine that we end up also in future to bugs allocation so
> it would have the script when you clone the kernel tree, and possibly
> more scripts in future.
> 
> E.g. add bt/alloc-error.bt under tools/testing/selftests/sgx.

Thank you very much for helping to debug this issue. I also think
the scripts you created are very valuable and making them easily
accessible sounds great.

Reinette