On Wed, Aug 29, 2018 at 06:45:29PM -0700, Huang, Kai wrote: > > > > > > Some kind of counter is required to keep track of the power cycle. > > > > > > When going to sleep the sgx_pm_cnt is increased. sgx_einit() > > > > > > compares the current value of the global count to the value in > > > > > > the cache entry to see whether we are in a new power cycle. > > > > > > > > > > You mean reset to Intel default? I think we can also just reset > > > > > the cached MSR values on each power cycle, which would be simpler, > > IMHO? > > > > > > > > Refresh my brain, does hardware reset the MSRs on a transition to S3 or > > lower? > > Sorry I missed this one. To be honest I don't know. I checked the SDM and all I can find is: > > "On reset, the default value is the digest of Intel's signing key." I confirmed the MSRs are reset any time the EPC is lost. Not sure what happens if the MSRs contained a non-Intel value but feature control is locked with SGX launch control disabled. I'll post an update when I have an answer. > Jarkko may know. > > > > > > > > > > I think we definitely need some code to handle S3-S5, but should > > > > > be in separate patches, since I think the major impact of S3-S5 is > > > > > entire EPC being destroyed. I think keeping pm_cnt is not > > > > > sufficient enough to handle such case? > > > > > > > > > > > > This brings up one question though: how do we deal with VM host > > > > > > going to > > > > sleep? > > > > > > VM guest would not be aware of this. > > > > > > > > > > IMO VM just gets "sudden loss of EPC" after suspend & resume in host. > > > > > SGX driver and SDK should be able to handle "sudden loss of EPC", > > > > > ie, co-working together to re-establish the missing enclaves. > > > > > > > > > > Actually supporting "sudden loss of EPC" is a requirement to > > > > > support live migration of VM w/ SGX. Internally long time ago we > > > > > had a discussion and the decision was we should support SGX live > > > > > migration given > > > > two facts: > > > > > > > > > > 1) losing platform-dependent is not important. For example, losing > > > > > sealing key is not a problem, as we could get secrets provisioned > > > > > again from remote. 2) Both windows & linux driver commit to > > > > > support "sudden > > > > loss of EPC". > > > > > > > > > > I don't think we have to support in very first upstream driver, > > > > > but I think we need to support someday. > > > > > > > > Actually, we can easily support this in the driver, at least for SGX1 hardware. > > > > > > That's my guess too. Just want to check whether we are still on the > > > same page :) > > > > > > > SGX2 isn't difficult to handle, but we've intentionally postponed > > > > those patches until SGX1 support is in mainline[1]. > > > > Accesses to the EPC after it is lost will cause faults. Userspace EPC accesses, > > e.g. > > > > ERESUME, will get a SIGSEGV that the process should interpret as an > > > > "I should restart my enclave" event. The SDK already does this. In > > > > the driver, we just need to be aware of this potential behavior and > > > > not freak out. Specifically, SGX_INVD needs to not WARN on faults that may > > have been due to a the EPC being nuked. > > > > I think we can even remove the sgx_encl_pm_notifier() code altogether. > > > > > > Possibly we still need to do some cleanup, ie, all structures of enclaves, upon > > resume? > > > > Not for functional reasons. The driver will automatically do the cleanup via > > SGX_INVD when it next accesses the enclave's pages and takes a fault, e.g. > > during reclaim. Proactively reclaiming the EPC pages would probably affect > > performance, though not necessarily in a good way. And I think it would be a > > beneficial to get the driver out of the suspend/hibernate/resume paths, e.g. > > zapping all enclaves could noticeably impact suspend/resume latency. > > Sure. > > Thanks, > -Kai >
