On Mon, Sep 16, 2019 at 11:01:43AM +0300, Jarkko Sakkinen wrote: > On Mon, Sep 16, 2019 at 10:58:06AM +0300, Jarkko Sakkinen wrote: > > On Mon, Sep 16, 2019 at 07:14:00AM +0300, Jarkko Sakkinen wrote: > > > My flush of updates for v23. Contains a bunch of clean ups and bug > > > fixes with the main focus on the page reclaimer. The main goal has > > > been to disclose all the other possibilities for failure after > > > ENCLS[EBLOCK] other than EPCM conflict when the whole EPC is > > > invalidated. > > > > I have at least one more update to the reclaimer but want to merge these > > first. > > > > It adds optional struct epc_page **reclaimed_page to > > sgx_reclaim_pages(). If NULL, the function will just append everything > > to the free pool. Otherwise, it will use it to return one of the > > reclaimed pages if there are any. > > > > sgx_alloc_page() then does the following when @reclaim=true: > > > > 1. If page in free page pool, take one. > > 2. If not, try to reclaim one. > > 3. If nothing was reclaimed -ENOMEM. > > > > Right now sgx_alloc_page() can in theory take however long. > > > > I wonder why we do not return -ENOMEM also when @reclaim=false. Where > > did this returning -EBUSY came from? Can't recall. > > Checked. I guess it is just for ELDU flow but does not make sense > otherwise. Tuning sgx_vma_fault() should be enough. I mean with > the above change we would start to return -EBUSY sometimes in > OOM situations. Returning -EBUSY is done to differentiate between the case where reclaim is possible, i.e. sgx_active_page_list is *not* empty, but disallowed, and the case where reclaim is impossible, i.e. sgx_active_page_list is empty. If reclaim is impossible then the fault handler should signal SIGSEGV so that processes start dying and/or killing enclaves to free up EPC. Barring a kernel bug, I don't think it's possible for sgx_active_page_list to be empty when only the driver is supported, but both KVM and EPC cgroup support will introduce (relatively common) scenarios where there are no pages on the active/reclaimable list. Technically we probably don't need the -EBUSY logic, but my vote is to keep it since it's a nice fallback in case there are kernel bugs.
