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From: Reinette Chatre <>
To: Jarkko Sakkinen <>
Cc: Shuah Khan <>,,,
	Borislav Petkov <>,
	Dave Hansen <>,
Subject: Re: [PATCH 4/4] selftests/sgx: Trigger the reclaimer and #PF handler
Date: Wed, 7 Jul 2021 14:20:04 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi Jarkko,

On 7/7/2021 1:50 PM, Jarkko Sakkinen wrote:
> On Wed, Jul 07, 2021 at 08:02:42AM -0700, Reinette Chatre wrote:
>> 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
> There is consistent known behaviour how reclaimer and also the page fault
> are exercised for each test. I think that is what matters most right now
> that the basic behaviour of both the page reclaimer and page fault handler
> gets exercised.

I believe the basic behavior of page fault handler is currently 
exercised in each test, this is required.

> I don't understand the real-world gain of doing something factors more
> complex than necessary at a particular point of time,  when you don't
> really need to hang yourself into it forever.

Your argument about "hang yourself into it forever" can go both ways - 
why should all tests now unnecessarily consume the entire EPC forever?

If I understand correctly adding a separate reclaimer test is not 
complex but would require refactoring code.

> This patch does increase the coverage in a deterministic manner to the code
> paths that were not previously exercised, i.e. we know the code paths, and
> could even calculate the exact number of times that they are triggered. And
> without doing anything obscure. That's what matters to me.

On the contrary this is indeed obfuscating the SGX tests: if an issue 
shows up in the reclaimer then all tests would fail. If there is a 
unique reclaimer test then that would help point to where the issue may be.


  reply	other threads:[~2021-07-07 21:20 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-05 14:36 [PATCH 0/4] selftests/sgx: Trigger the page reclaimer and #PF handler Jarkko Sakkinen
2021-07-05 14:36 ` [PATCH 1/4] x86/sgx: Add sgx_nr_all_pages to the debugfs Jarkko Sakkinen
2021-07-06 14:56   ` Dave Hansen
2021-07-06 15:39     ` Greg KH
2021-07-06 22:08     ` Jarkko Sakkinen
2021-07-05 14:36 ` [PATCH 2/4] selftests/sgx: Fix Q1 and Q2 calculation in sigstruct.c Jarkko Sakkinen
2021-07-06 20:53   ` Dave Hansen
2021-07-06 23:52     ` Jarkko Sakkinen
2021-07-05 14:36 ` [PATCH 3/4] selftests/sgx: Assign source for each segment Jarkko Sakkinen
2021-07-05 14:36 ` [PATCH 4/4] selftests/sgx: Trigger the reclaimer and #PF handler Jarkko Sakkinen
2021-07-06 18:34   ` Reinette Chatre
2021-07-06 23:50     ` Jarkko Sakkinen
2021-07-07  0:10       ` Reinette Chatre
2021-07-07  9:17         ` Jarkko Sakkinen
2021-07-07 15:02           ` Reinette Chatre
2021-07-07 20:50             ` Jarkko Sakkinen
2021-07-07 21:20               ` Reinette Chatre [this message]
2021-07-09 16:22                 ` Jarkko Sakkinen
2021-07-07 21:20               ` Dave Hansen
2021-07-09 16:25                 ` Jarkko Sakkinen

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