Thomas, > > > Aside of the condition being pointless in that case, that issues an IPI > whether the task is running or not. So this allows a task to issue tons of > async IPIs disturbing others by toggling the control.
I'm not crazy about sending IPIs too. Hence the original implementation using TIF_UPDATE_SPEC_CTRL flag. I've thought a bit about the options you suggested and was unclear on a few things. > 1) Restrict the PRCTL control so it is only possible to modify it at the > point where the application is still single threaded. > My understanding is PRCTL applied on the task only. Should it be extended to other task threads? In that case, it seems like we didn't do that for SSBD? > 2) Add _TIF_UPDATE_SPEC_CTRL to the SYSCALL_EXIT_WORK_FLAGS and handle it > in the slow work path. There can be tasks that don't do any syscalls, and it seems like we can have MSRs getting out of sync? > > I'm less and less convinced that piggybacking this on dumpable is a good > idea. There are daemons like sshd that are non-dumpable. So I think protecting them is desired. Otherwise all those daemons will need to be updated to use PRCTL. In the original implementation, IBPB is issued for non-dumpable task. It will be nice to retain that. Thanks. Tim
