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

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Date:   Tue, 6 Jul 2021 17:10:38 -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 7/6/2021 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