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

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Date:   Tue, 6 Jul 2021 11:34:54 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc:     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 7/5/2021 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