linux-kernel - Re: [PATCH 4/4] selftests/sgx: Trigger the reclaimer and #PF handler

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Date:   Wed, 7 Jul 2021 08:02:42 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-sgx@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] selftests/sgx: Trigger the reclaimer and #PF handler

Hi Jarkko,

On 7/7/2021 2:17 AM, Jarkko Sakkinen wrote:
> On Tue, Jul 06, 2021 at 05:10:38PM -0700, Reinette Chatre wrote:
>> Hi Jarkko,
>>
>> On 7/6/2021 4:50 PM, Jarkko Sakkinen wrote:
>>> On Tue, Jul 06, 2021 at 11:34:54AM -0700, Reinette Chatre wrote:
>>>> Hi Jarkko,
>>>>
>>>> On 7/5/2021 7:36 AM, Jarkko Sakkinen wrote:
>>>>> Create a heap for the test enclave, which has the same size as all
>>>>> available Enclave Page Cache (EPC) pages in the system. This will guarantee
>>>>> that all test_encl.elf pages *and* SGX Enclave Control Structure (SECS)
>>>>> have been swapped out by the page reclaimer during the load time. Actually,
>>>>> this adds a bit more stress than that since part of the EPC gets reserved
>>>>> for the Version Array (VA) pages.
>>>>>
>>>>> For each test, the page fault handler gets triggered in two occasions:
>>>>>
>>>>> - When SGX_IOC_ENCLAVE_INIT is performed, SECS gets swapped in by the
>>>>>      page fault handler.
>>>>> - During the execution, each page that is referenced gets swapped in
>>>>>      by the page fault handler.
>>>>>
>>>>
>>>> If I understand this correctly, all EPC pages are now being consumed during
>>>> fixture setup and thus every SGX test, no matter how big or small, now
>>>> becomes a stress test of the reclaimer instead of there being a unique
>>>> reclaimer test. Since an enclave is set up and torn down for every test this
>>>> seems like a significant addition. It also seems like this would impact
>>>> future tests of dynamic page addition where not all scenarios could be
>>>> tested with all EPC pages already consumed.
>>>>
>>>> Reinette
>>>
>>> Re-initializing the test enclave is mandatory thing to do for all tests
>>> because it has an internals state.
>>>
>>
>> Right, but not all tests require the same enclave. In kselftest terminology
>> I think you are attempting to force all tests to depend on the same test
>> fixture. Is it not possible to have a separate "reclaimer" test fixture that
>> would build an enclave with a large heap and then have reclaimer tests that
>> exercise it by being tests that are specific to this "reclaimer fixture"?
>>
>> Reinette
> 
> Why add that complexity?
> 

With this change every test is turned into a pseudo reclaimer test 
without there being any explicit testing (with pass/fail criteria) of 
reclaimer behavior. This is an expensive addition and reduces the 
scenarios that the tests can exercise.

Reinette