Messages in this thread | | | Subject | Re: [PATCH 4/4] selftests/sgx: Trigger the reclaimer and #PF handler | From | Reinette Chatre <> | Date | Wed, 7 Jul 2021 14:20:04 -0700 |
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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.
Reinette
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