On Tue, Sep 17, 2019 at 10:08:31PM +0300, Jarkko Sakkinen wrote: > On Mon, Sep 16, 2019 at 11:37:43AM -0700, Sean Christopherson wrote: > > 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. > > OK, my root question is I guess, why want to differentiate those cases? > Both are as far as I'm concerned situations where there is no memory > available. > > And now my changes after these patches add yet another case: active > page list was not empty but nothing could be reclaimed. Is the > granularity really needed for something here? Yes. If there are reclaimable pages, then letting userspace re-fault is correct as the process can make forward progress. Restarting userspace when there are no reclaimable pages will soft hang userspace, i.e. it'll fault indefinitely.
